Added addEffect method which got deleted before the commit
Added addEffect method which got deleted before the commit

--HG--
branch : feature/posteffects

sanyaade-teachings/engine,sanyaade-teachings/engine,MicroWorldwide/PlayCanvas,MicroWorldwide/PlayCanvas,aidinabedi/playcanvas-engine,shinate/engine,sereepap2029/playcanvas,horryq/engine-1,sereepap2029/playcanvas,nizihabi/engine,3DGEOM/engine,nizihabi/engine,guycalledfrank/engine,sereepap2029/playcanvas,H1Gdev/engine,playcanvas/engine,maxwellalive/engine,3DGEOM/engine,aidinabedi/playcanvas-engine,shinate/engine,shinate/engine,RainsSoft/engine,RainsSoft/engine,nizihabi/engine,RainsSoft/engine,sanyaade-teachings/engine,horryq/engine-1,SuperStarPL/engine,H1Gdev/engine,SuperStarPL/engine,3DGEOM/engine,playcanvas/engine,SuperStarPL/engine,maxwellalive/engine,guycalledfrank/engine,maxwellalive/engine,horryq/engine-1