Blender Git Loki

Fix T50491: Cycles UI breaks when pushing F8.

Cycles add-on did not actually support reloading correctly.

When you want to correctly reload sub-modules (i.e. modules of an add-on
which is a package), you need to use importlib, a mere import will do
nothing with already loaded modules (RNA classes are sort of
pre-registered when they are evaluated, through the meta-class system).