Added documentation on light brightness and negative lights.
Apply node transform to collision shape, add CollisionCircle2D.[ci skip]
Merge remote-tracking branch 'upstream/master'

Conflicts:
	Source/Samples/27_Urho2DPhysics/Urho2DPhysics.cpp
	Source/Samples/27_Urho2DPhysics/Urho2DPhysics.h