Fixes Timeout When Adding an SSH key with Many Projects 

Users with many projects (>100) will hit the 20 second timeout when
updating the gitolite config. This fix batches those changes into a
signle update to the file, causing an order of magnitude speed increase
which finishes well below the 20 second timeout.

Fixes gitlabhq/gitlabhq#220

This reverts commit f80745b7.

Project destroy relationship speed fix

Removes destroy callback for users_projects when a project is destroyed.
This works okay becaues the gitolite config will be updated at at the
end to remove the entry entirely, thereby removing the users anyway.

Bulk repo import Rake task