Expression support, including ChangeVar effect
 - Can parse, evaluate and serialize strongly-typed expressions
 - Implements most common operations (easily extensible)
 - Caches constant results to avoid re-evaluation
 - Throws nice exceptions to complain about runtime evaluation problems

Expressions can be built by parsing a lisp-like representation
(see Parser.parse()) or composing Literals, VariableRefs, and Operations

Expressions are evaluated by calling evaluate() on a given VarsContext
Added new strings
Added StyleName for OptionPanel
Added OptionsWidgetPanel
Fixed small typo.
Added file headers
Fixed some issues with Table#drawBackground
Generate languages dynamically
Renamed some classes.
Renamed some classes
Renamed LateralPanelStyle to HiddenPanelStyle
Some minor changes
Removed not longer needed StyleName from json.
Removed StyleName dependency from HiddenPanel.
Fixed small bug that made the HiddenPanel not to hide if FADE_TIME was 0.
Changed it's animation to FadeIn/Out.
Fixed a bug that let the input signal to pass through even if the panel was modal.
Added lateral transitions on show/hide for LateralOptionsPanel.
Renamed HiddenPanel attribute,
no need to invoke rectangle.contains() if hideOnExternalTouch is false.
Added change language  functionality to LateralOptionsPanel.
Added shange skin functionality to LateralOptionsPanel.
Since there aren't various skins to test,
we can only change to the "default" skin and
go to MainBuilder.