Made the grid in BrickMap smaller until performance can be improved
Made left-click add a gold brick
Made right-click remove a gold brick
Use BoxComponents to show where the bricks will be created/destroyed

Work around plugin/blueprint loading order problems:
* Add GameMode blueprint
* Replace C++ GameMode reference to MyCharacter blueprint with a reference from the blueprint GameMode
* Allows MyCharacter to reference BrickGridComponent class in the BrickGrid plugin, which isn't loaded yet if MyCharacter is loaded with the C++ game code
Made BrickGrid plugin name consistent with the other plugins (doesn't include the word plugin)