gitlab: added new app:rake command to run rake tasks
gitlab: removed the "app:backup" command, "app:rake gitlab:backup:create" is now used to create a backup
gitlab: removed the "app:restore" command, "app:rake gitlab:backup:restore" is now used to restore a backup
gitlab: removed the "app:db:migrate" command, "app:rake db:migrate" is now used for migration
gitlab: removed the "app:db:initialize" command, "app:rake gitlab:setup" is now used for initialization
Merge branch 'feature/raketasks'
gitlab: pass all parameters supplied to app:rake to rake_task function
README: fixed backup command in upgrade instructions
README: add -rm option to intermediate commands