Playground page for transformers and formatters

[Kentzo]

The playground should show that:

• The SRKeyCodeTransformer class cluster can turn a key code and a shortcut into a string
• SRASCIILiteralKeyCodeTransformer can perform reverse transformations
• The SRModifierFlagsTransformer class cluster can turn modifier flags and a shortcut into a string
• SRSymbolicModifierFlagsTransformer allows reverse transformations
• SRKeyEquivalentTransformer can turn both a shortcut and it dictionary representation into Cocoa's key equivalent string
• SRKeyEquivalentModifierMaskTransformer can turn both a shortcut and its dictionary representation into Cocoa's key equivalent modifier mask.