Merge pull request #30 from playcanvas/master

memeem
Merge pull request #31 from playcanvas/master

merge
Particle fixes.

Fixed alignToMotion;
Added check for more than 65k verts in particle system;
Fixed gamma correction on particles in some conditions;
Fixed particle shader caching key generation;
Fixed runtime CPU-GPU particle switch;
Fixed sorting of mesh particles;
wrapBounds are now relative to emitter pos instead of camera pos;
mode parameter now uses enum, not string;
Fixed mobile particle problems;
Depth softening control is now a bit more intuitive;
Added _activeCamera to scene object (actually last rendered camera);
Fixed depth softening bugs;
Removed camera property from particle system.
Shortened particle enum names
Removed unnecessary code
Merge pull request #113 from guycalledfrank/particle-fixes-new

Particle fixes new