Add basic per Material scissor testing

It is now possible to enable and specify scissoring on a per
Material basis using getAdditionalRenderState(). Currently
only works for single ViewPort.
Merge branch 'master' of https://github.com/jMonkeyEngine/jmonkeyengine into scissor

Conflicts:
	.gitignore
	jme3-lwjgl/src/main/java/com/jme3/renderer/lwjgl/LwjglRenderer.java
Add support for scissor intersections

If a per Material scissoring is specified the resulting scissor area
will be the intersection of that scissor rectangle and any
existing scissor rectangle applied with setClipRect()
Add per Material scissoring support to all Renderers

The per Material scissoring support is now included in the remaining
Renderers.
Merge branch 'scissor'