NumberGame introduced

Takes a load of the Subgame class. Intended to facilitate additional
game variants that do not depend upon a single number as the correct
answer.
Major re-write. All games now use NumberGame

The common functionality in NumberGame is more easy to use for the
current games. But future games might have other needs. So it has been
broken out into its own class. It is now optional to setup button
panels.
Moved files
NumberGame: Create only relevant buttons
Balloon: Rewrite for NumberGame structure 1

* Restructured the balloon stacks to be their own object.
* Hack & / variables and sprite creation.
Balloon: Rewrite for NumberGame structure 2

Graphics update.
Balloon: Rewrite for NumberGame structure 3

Hack & /.
These changes break some of the methods. But I intend to repair them
again.
NumberButton has a sprite representation variant
NumberGame: Touch up for when not using panels
Balloon: Rewrite for NumberGame structure 4

Almost complete. Partitioned most of the functions into prototype
instead.
Balloon: Rewrite for NumberGame structure 5

Added the different methods. Final rewrite hopefully :)
Balloon: Fine tuning and bug fixing
Bigger thought button
Removed unnecessary calls
Representation: Removed unused

SignedNumberRepresentation was no longer used.
SpriteRepresentation is the same as object.
Subgame comments update
Buttons: New graphics and functionality

It is now possible to change the color of a button.
Buttons: Update to new, remove old
Garden: Removed drop from graphics
New graphics update 1

Watering can, water drop, garden and volume button.