Event invites

Added the view and controller to deal with the event invites. No backend
logic yet.
Controller refactoring

Controllers that all need a "navigateMenu" function now inherit this
function from a superclass. Controllers all follow the same naming
convention. (When the panel is called ViewFriendsPanel, the controller
will be ViewFriendsController rather than ViewFriendsPanelController).

Included try-catch logic in the AddFriendController.