Added Scalingo compatible deployment

Signed-off-by: Brandon WELSCH <dev@brandon-welsch.eu>

.buildpacks

+https://github.com/alex88/heroku-buildpack-vips
+https://github.com/Scalingo/nodejs-buildpack

scalingo.json

+{
+    "name": "CodiMD",
+    "description": "Realtime collaborative markdown notes on all platforms",
+    "keywords": [
+        "Collaborative",
+        "Markdown",
+        "Notes"
+    ],
+    "website": "https://github.com/hackmdio/codimd",
+    "repository": "https://github.com/hackmdio/codimd",
+    "logo": "https://github.com/hackmdio/codimd/raw/master/public/codimd-icon-1024.png",
+    "success_url": "/",
+    "env": {
+        "NPM_CONFIG_PRODUCTION": {
+            "description": "Let npm also install development build tool",
+            "value": "false"
+        },
+        "CMD_SESSION_SECRET": {
+            "description": "Secret used to secure session cookies.",
+            "required": false
+        },
+        "CMD_HSTS_ENABLE": {
+            "description": "whether to also use HSTS if HTTPS is enabled",
+            "required": false
+        },
+        "CMD_HSTS_MAX_AGE": {
+            "description": "max duration, in seconds, to tell clients to keep HSTS status",
+            "required": false
+        },
+        "CMD_HSTS_INCLUDE_SUBDOMAINS": {
+            "description": "whether to tell clients to also regard subdomains as HSTS hosts",
+            "required": false
+        },
+        "CMD_HSTS_PRELOAD": {
+            "description": "whether to allow at all adding of the site to HSTS preloads (e.g. in browsers)",
+            "required": false
+        },
+        "CMD_DOMAIN": {
+            "description": "domain name",
+            "required": false
+        },
+        "CMD_URL_PATH": {
+            "description": "sub url path, like `www.example.com/<URL_PATH>`",
+            "required": false
+        },
+        "CMD_ALLOW_ORIGIN": {
+            "description": "domain name whitelist (use comma to separate)",
+            "required": false,
+            "value": "localhost"
+        },
+        "CMD_PROTOCOL_USESSL": {
+            "description": "set to use ssl protocol for resources path (only applied when domain is set)",
+            "required": false
+        },
+        "CMD_URL_ADDPORT": {
+            "description": "set to add port on callback url (port 80 or 443 won't applied) (only applied when domain is set)",
+            "required": false
+        },
+        "CMD_FACEBOOK_CLIENTID": {
+            "description": "Facebook API client id",
+            "required": false
+        },
+        "CMD_FACEBOOK_CLIENTSECRET": {
+            "description": "Facebook API client secret",
+            "required": false
+        },
+        "CMD_TWITTER_CONSUMERKEY": {
+            "description": "Twitter API consumer key",
+            "required": false
+        },
+        "CMD_TWITTER_CONSUMERSECRET": {
+            "description": "Twitter API consumer secret",
+            "required": false
+        },
+        "CMD_GITHUB_CLIENTID": {
+            "description": "GitHub API client id",
+            "required": false
+        },
+        "CMD_GITHUB_CLIENTSECRET": {
+            "description": "GitHub API client secret",
+            "required": false
+        },
+        "CMD_GITLAB_BASEURL": {
+            "description": "GitLab authentication endpoint, set to use other endpoint than GitLab.com (optional)",
+            "required": false
+        },
+        "CMD_GITLAB_CLIENTID": {
+            "description": "GitLab API client id",
+            "required": false
+        },
+        "CMD_GITLAB_CLIENTSECRET": {
+            "description": "GitLab API client secret",
+            "required": false
+        },
+        "CMD_GITLAB_SCOPE": {
+            "description": "GitLab API client scope (optional)",
+            "required": false
+        },
+        "CMD_MATTERMOST_BASEURL": {
+            "description": "Mattermost authentication endpoint",
+            "required": false
+        },
+        "CMD_MATTERMOST_CLIENTID": {
+            "description": "Mattermost API client id",
+            "required": false
+        },
+        "CMD_MATTERMOST_CLIENTSECRET": {
+            "description": "Mattermost API client secret",
+            "required": false
+        },
+        "CMD_DROPBOX_CLIENTID": {
+            "description": "Dropbox API client id",
+            "required": false
+        },
+        "CMD_DROPBOX_CLIENTSECRET": {
+            "description": "Dropbox API client secret",
+            "required": false
+        },
+        "CMD_DROPBOX_APP_KEY": {
+            "description": "Dropbox app key (for import/export)",
+            "required": false
+        },
+        "CMD_GOOGLE_CLIENTID": {
+            "description": "Google API client id",
+            "required": false
+        },
+        "CMD_GOOGLE_CLIENTSECRET": {
+            "description": "Google API client secret",
+            "required": false
+        },
+        "CMD_IMGUR_CLIENTID": {
+            "description": "Imgur API client id",
+            "required": false
+        },
+        "CMD_ALLOW_PDF_EXPORT": {
+            "description": "Enable or disable PDF exports",
+            "required": false
+        },
+        "CMD_DB_URL": {
+            "description": "Database query url",
+            "value": "$DATABASE_URL"
+        },
+        "DYNO": {
+            "description": "Require this env var for deploy correctly the app",
+            "value": "Scalingo"
+        }
+    },
+    "formation": {
+        "web": {
+            "amount": 1,
+            "size": "S"
+        }
+    },
+    "addons": [
+        "postgresql:postgresql-sandbox"
+    ]
+}