Handle custom iOS AppDelegate

[binouze]

Handle projects with custom iOS app delegate, by commenting the App Delegate directive in the SingularAppDelegate.m file

• Added a menu inside Window/Singular to set if iOS app uses a custom AppDelegate or not and saves the value in an EditorPref variable.
• If iOS app uses a custom AppDelegate, comment out the IMPL_APP_CONTROLLER_SUBCLASS directive in SingularAppDelegate.m file after the build.