Fixed the lint issues in the QuadTree library
Simplified the QuadTree implementation

We have no use for pointQuad support anyway (and both mode cannot be
mixed), and this will simplify debugging (as currently the quadtree
library keeps returning ALL objects......)
[#394] updated examples with the new collision API

also made the slimEntity "solid" in the platformer using the given
response object
fixed a bunch of whitespace /TAB issues in the examples
splitting/renaming source code for better clarity
[#480] renamed `me.SpriteObject` to `me.Sprite` and `me.ObjectContainer` to `me.Container`
[documentation] made the quadtree "private"
`addChild` and `addChildAt` now return the added child

(as discussed on the forum)