Convention.py

Convention.py is a module that provides plugins for basic programming convention checks. It includes SpriteNaming class, a plugin that keeps track of how often sprites default names (like Sprite1, Sprite2...) are used. 

Add conditional statement in duplicate.DuplicateScripts so scripts defined by user are not considered.

Update the strings in the BLOCKMAPPING to match Kurt 2 block.type.text, fixing issue https://github.com/ucsb-cs-education/hairball/issues/5