setProp and getProp handler execution for engine properties functional but not completely tested
skipping get props and septrops on properties that are references to the object
Merge branch 'feature/engine_getprop_setprop' of https://github.com/montegoulding/livecode into monte-engine_getprop_setprop

Conflicts:
	engine/src/control.cpp
	engine/src/graphic.cpp
	engine/src/objectprops.cpp
Merge branch 'monte-engine_getprop_setprop' into feature-engine_getprop_setprop

Conflicts:
	engine/src/object.h
	engine/src/objectprops.cpp
[[ EngineProps ]] Moved message send for engine messages from _legacy methods to set/getprop methods.
[[ EngineProps ]] Renamed original sendsetprop/sendgetprop to sendcustomsetprop/sendcustomgetprop to distinguish from keyword sendsetprop/sendgetprop.
[[ EngineProps ]] Initial definition of methods to unify setprop/getprop handling.