prevent possible NPE
fix keyboard navigation in change list

- inverse check of ListSelectionEvent#getValueIsAdjusting
add action to checkout selected change

- use currently selected revision in fetch action (used in compare branch, cherry-pick and checkout)

Resolves #82
update gerrit-rest-java-client submodule
enable notification balloons again

- review and error notifications got lost after refactoring
bump version to v0.9.3
Merge remote-tracking branch 'origin/master' into intellij13