asynchronously load data from Gerrit

- do not block UI

Resolves #28
add separator after filter actions
cleanups

- add licence headers
- optimize imports
show own review notifications for all project

- restore "old" behavior (before filter refactoring)
- prevents startup warning that no git repositories are available (looks like initialization is done afterwards)
fix submitting from review action

- submit must happen after review (got broken because of asynchronous Gerrit operations)
- submit-action: change info is enough to get id (change details are not required)
fixes and improvements for file comments

- load comments asynchronously
- display newly created comments (in review comment sink) in corresponding file only
- show comment action and comments also after switching to next file (instead of opening review dialog again)