feat(contenedit): $rootScope.$on unregistration in Controllers

The controllers that have registered an event on the rootscope
unregister this now in $scope.$on destroy to prevent from memoryleaks
and unwanted message handling
feat(contentedit): improved the error handling and logging in githubContentProvider
feat(contentedit): CommitDlg ctrl sends now the message directly to the contentCtrl
refact(directives) some small code polish
feat(contentedit): Shortcut for edit changed

The shortcut for edit is now just e to prevent from shortcut collisions on windows
feat(contentedit): ContentCtrl checks now if edit is allowed