Combine DrawableProxy2D and MaterialCache2D in to Renderer2D.
Remove Sprite2D from Drawable2D, make Drawable2D more general.
Remove custom material from Drawable2D, Renderer2D will get all Drawable2D when HandleBeginViewUpdate.
rename DRAWABLE_PROXYGEOMETRY DRAWABLE_RENDERER2D
Fix bug.
Remove unused code, rename DefaultMaterial to Material.
Fixed tile map remove layer node bug.
For Travis CI - switch CI build to use Android build environment.