Rename Commit#revision to Commit#sha for git

Since we are only supporting git right now, stick to semantics and give
the column a git-specific name for a revision: sha.
Use Bootstraps's defaults in preparation for Bootstrap 3
Improve aesthetics the developers index
Auto compact nils from #in_groups_of
Give commits a fake sha in populate task

[ci skip]
Display the commit sha on the wall display
Updating the screenshot
Improve the projects index page