readability fixes (don’t use std::pair a gogo + more readable use of std::map) + memory leak (tryInstance was not freed in some cases)
memory leak: if there is no associated node, the effect_ member was not deleted. ANYWAY the handling of effect_ is just CRAZY (created here, but « owned » by Node????)
fix default value for kOfxParamPropParametricRange
fix memory craziness and slow startup time.
write the OFX plugin cache as soon as it has been filled (why wait so long?)
Merge branch 'workshop' of https://github.com/MrKepzie/Natron into workshop

Conflicts:
	Engine/OfxHost.cpp