Expose a commit's branch in a few different places:

* Add branch name to the file / directory history.
* Added getBranch() to the CommittedChangeList, allowing easy determination of which branch the changelist happened on. May return null if not applicable. Check the branch of the changelist when rendering the changes; if non-empty, make the branch visible to the user. Very helpful when looking at all changes.
* When custom ChangeListColumns are added to the Repository table, and that column has a comparator, it will be added as an option for grouping. In particular, for Mercurial you can now view the Repository tab grouped by Branch.