Find a unifying prefix?

[tinchodias]

There is currently:

• MG (e.g. MGGame)
• DT (e.g.DTPaneCreatingReorderingHandler)
• Br (some Brick subclasses)

[StephanEggermont]

DT comes from DrawingTool, but a common prefix makes sense indeed

[tinchodias]

I did it in #9

(renamed to Bl)