Expand checkSceneLights() function for use 'meshlights' with Bidirectional integrator
Review checkSceneLights() from 'wizofboz' feedback:
    - separate background check to objects.
    - add check for portal lights objects.
Fix AO issue (wizofboz):
    -Fixed error of indentation in 'yaf_integrator.py'
    causer of the error in the use of Ambient Occlusion.
Merge branch 'master' into merge_SSS

Conflicts:
	io/yaf_integrator.py
Solve conflict for fix indentation error in AO
after merge from master