[[ Bug 13021 ]] Add MCGRectangleScale variant with horiz/vert params
[[ ImageLoader ]] Add frame count to information read from the header.
[[ ImageLoader ]] Use header framecount for MCEncodedImageRep::GetFrameCount()
Merge remote-tracking branch 'runrevian/refactor-imageloader' into bugfix-13021

Conflicts:
	engine/src/ibmp.cpp
	engine/src/igif.cpp
	engine/src/ijpg.cpp
	engine/src/image_rep.cpp
	engine/src/image_rep.h
	engine/src/imageloader.cpp
	engine/src/ipng.cpp
[[ Bug 13021 ]] Add bugfix note