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 4 minutes and 23 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
passed test #7738
container

00:01:57

 
  Prod Setup
passed prod_setup_check #7739
container

00:02:26