cleanup gemfile + introduce gitlab ci

* Remove some unneeded deps
* Add gitlab ci similar to how users has, although currently we do
  have any proper tests, it still checks something
* Introduce a ci task that runs the steps to prepare the app after
  checkout from git
2 jobs for add-ci-cleanup-gemfile in 1 minute and 17 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
failed test #7701
container

00:01:17

 
  Prod Setup
skipped prod_setup_check #7702
container
 
Name Stage Failure
failed
test Test
In Gemfile:
rails was resolved to 5.2.4.4, which depends on
actioncable was resolved to 5.2.4.4, which depends on
actionpack was resolved to 5.2.4.4, which depends on
actionview was resolved to 5.2.4.4, which depends on
rails-dom-testing was resolved to 2.0.3, which depends on
nokogiri
Cleaning up file based variables
ERROR: Job failed: exit code 1