Cleanup MapInfo

[pauldendulk]

• Make MapInfo non-nullable. This was easy to fix in the core and avoids having to pass the nullable MapInfo to many other method.
• Use TapType in MapInfo
• Some renaming from Info to MapInfo, but not yet on the event, perhaps I should rename that as well.
• Add GetMapInfo() to the WidgetEventArgs to make it easy to call from all events. By adding it as a method it will not affect performance unless users will actually call the GetMapInfo(). I am considering adding a list of layer to query as argument and remove the ILayer.IsInfoLayer.
• Cleanup LabelsSample.cs (completely unrelated)