Added in a UIStyle system.
Merge branch 'restructure' of git@github.com:MovingBlocks/Terasology.git into restructure
Implemented Skinning system for ui components. A skin works in a similar way to a CSS - it contains style options for combinations of widget types, the current mode of those types (e.g. buttons being hovered over or held down), and a family (e.g. main menu buttons vs inventory buttons).  The style features are all used by the canvas when rendering element text, texture or background.
Merge branch 'restructure-ui' into restructure

Conflicts:
	engine/src/main/java/org/terasology/rendering/gui/windows/UINUITest.java
	engine/src/main/java/org/terasology/rendering/nui/LwjglCanvas.java
Merge branch 'restructure' of git@github.com:MovingBlocks/Terasology.git into restructure
Added support for AssetResolvers, for providing access to assets which don't correspond to individual files.
Added Rect2f
Added TextureAtlas asset support - this describe a mapping of a texture into a number of Subtextures
Added Subtexture asset type
Implemented support for Subtextures to NUI.
Some improvements to WorldTime events.
Added items texture atlas.