Fix GerritGitUtil for IDEA 135

JetBrains/intellij-community@d6528d34d2e7e8524ef6de11a64eb6ec16ff28aa refactored UntrackedFilesNotifier to not require the PlatformFacade any more. This change brings gerrit-intellij-plugin inline with Intellij 13.1 and fixes issue #62.