Change the filter factory to be more a provider.
The Filter provider now initialises a Filter and
put them into a local cache object. With this we
avoid to create a new Filter object every time
we need a Filter. In addition, now we are able to
use some caching mechanism for commit fetching.
* remove obsolete contributor attribute and it’s 
  setter from Filter
* add commit caching for a single page request to filter
* add methods to get a contributor and a branch list
  of the current repo to filter
* reset the commit cache every time a change is
  happened to the filter
#87 Refactor filter controller 

* filter controller now takes care if we want to
  display an existing Filter or a new one
* don’t set $scope attributes before every required
  call is done
* add a comment to Filter to investigate commit
  handling if commit has no author attribute
* rename addFilter.html template to filter.html
* code formatting
* add caching of repositories and branch fetching in service methods
* remove obsolete module injection from commit header directive
* edit and add filter now uses the filter.html template
* replace the commit list controller and also the commit list template
  with the filter controller and the filter template
Create a directive for the commit list now we can
reuse the commit list
* fix commit list template to work with the new directive
* use html5 conform attribute naming
* remove obsolte commit list controller
* move commit list directive to own file
* add own controller to commit list directive
* pass filter and commit list to commit list directive scope
* add approved commits to commit list directive
Separate oauth callback handling from main application

* add oauth callback page
* remove weird oauth callback handling from root controller
* change oauth callbck url in options for dev mode
* combine both menu templates