[[ ImageLoader ]] Create MCImageLoader class interface
[[ ImageLoader ]] Reimplement MCImageDecode<format> functions as equivalent MCImageLoader subclasses
[[ ImageLoader ]] Update Image import functions to use MCImageLoader
[[ ImageLoader ]] Fix bug in IO_fgets causing inifinite loop when loading xpm file
[[ ImageLoader ]] Update Android, iOS, Linux & OSX server build files
[[ ImageLoader ]] Update Windows engine & server build files
Merge remote-tracking branch 'runrevian/refactor-imageloader' into bugfix-13021

Conflicts:
	engine/engine.xcodeproj/project.pbxproj
	engine/src/ifile.cpp
	engine/src/igif.cpp
	engine/src/iimport.cpp
	engine/src/image.h
	engine/src/image_rep_encoded.cpp
[[ Bug 13021 ]] Rework MCImage::lockbitmap() MCImage::draw() to allow density-mapped images to have mismatched scale & image sizes.
[[ Bug 13021 ]] Modify MCDensityMappedImageRep::GetGeometry() to return logical image size for the whole set.
[[ Bug 13021 ]] Remove unused density & scale methods from MCImage & MCImageRep classes
[[ 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
[[ Bug 13058 ]] Use Stack view rect when determining if pointer is still within stack window
Play selection respects the selectionEnd point
[[ Bug 13063 ]] Fixed first part of bug 13063 (i.e. setting startTime to the correct point)
[[ Bug 13096 ]] Resolve relative initial path before passing to file / folder dialogs
[[ Bug 13038 ]] Use platform-specific methods of obtaining random bytes, rather than rely on SSL
[[ Bug 13064 ]] playSelection respects start/end point. However a delay in pause appears when EndTimeChanged is called too often
Removed unused code
[[ Bug 13059 ]] Enable MCStack::menumup() actions for menuname stacks
Merge remote-tracking branch 'ian/bugfix-13059' into bugfix-13059
Merge branch 'bugfix-13059' into release-6.6.3