feat(semantic-release): sort changelog on `commitTypes` order

The sorting of changelog section is done alphabetically on the commit
type by default.

* .releaserc.js (commitGroupsSortFn): sort commits based on their type
  order in `commitTypes` array: type at the beginning of the array is
  first in the changelog output.
  (commitTypes): reorder the array to have `Features` first and
  `Maintenance` last.
  (@semantic-release/release-notes-generator): configure
  `commitGroupsSort` with our `commitGroupsSortFn` function.