Added instance cache to recycle deleted instances.
Adapted RuntimeObject to avoid recreating members objects if not needed.
Some classes still needs recycling ( gdjs.Polygon... )
Various optimizations
Avoid arrays creation in polygon.js
Textures of SpriteRuntimeObject were always updated even when not necessary.
Avoid variable creation/destruction in variablescontainer.js.
Avoid calling Array.remove when running an object or automatism condition.
Various micro optimizations.
And ensure the canvas has the focus on IE9.
Optimized scene and global variables lookup when the variables are declared.