Layer refactoring... not finish yet.

Cannot compile now.
Step 1, compile ok.
..
Step 2. re-implement LayerImage
Try to remove LayerImage, use Layer instead.
1 more unit test
Merge branch 'dev' into refactor/layer
Merge branch 'dev' into refactor/layer

Conflicts:
	src/external/win32/win32.cpp
	src/graphics/bitmap/bitmapimage.h
	src/graphics/vector/vectorimage.cpp
	src/graphics/vector/vectorimage.h
	src/interface/backupelement.h
	src/interface/editor.cpp
	src/interface/editor.h
	src/interface/mainwindow2.cpp
	src/interface/mainwindow2.ui
	src/interface/scribblearea.cpp
	src/managers/layermanager.cpp
	src/structure/camera.cpp
	src/structure/camera.h
	src/structure/keyframe.cpp
	src/structure/keyframe.h
	src/structure/layer.cpp
	src/structure/layer.h
	src/structure/layerbitmap.cpp
	src/structure/layerbitmap.h
	src/structure/layercamera.cpp
	src/structure/layercamera.h
	src/structure/layerimage.cpp
	src/structure/layerimage.h
	src/structure/layersound.cpp
	src/structure/layersound.h
	src/structure/layervector.cpp
	src/structure/layervector.h
	src/structure/object.cpp
	src/util/util.h
add lost files
Merge branch 'refactor/layer' into dev