Drop satellites

So far this merge request does not affect UI or UX. Actually it affects UX only in one way -> stuff works faster sometimes

What this merge request does:

• remove all source code related to satellites (duplicate of repo for diff between forks)
• fetch branch from fork into refs/merge-requests/:id/head of original repo when create merge request
• fetch branch from fork into refs/tmp/:randomhex/head of original repo when do compare between forks
• use gitlab_git and rugged libs to deal with compare and merge changes

This merge request does not affect wiki since we dont use satellites with wiki feature!

This merge request does not remove satellites directory and leave config settings for it. I am going to remove it in 8.0 after we confirm its not needed any more - #2186 (closed).