Also specify separate project factory for project with filled repo

Add Repository model to proxy request to Gitlab::Git::Repositoty and decorate commits with Commit model

Use existing methods for branch names: Ex use @repository.branch_names instead of @repository.heads.map(&:name)

This reverts commit 4524ba20.

I discovered while trying to use UserTeam#remove_member() that
UsersProject.in_projects was broken.  So I wrote test cases to test what
I was trying to do and fixed the underlying problem.