Make branches first class citizens

[vladak]

When working on issue #865 I noticed that repository object does not track branches. It might make sense to add a getBranch() method (and private member) which would return current branch (if the repo supports it). With that it would be possible e.g. to have the branch listed on the index page (once this is made so the list of projects with descriptions etc. is automatically generated on the front page = issue #470 and such).