Move frame search task to DrawableLayer
Separate frame compositing function, prepare it for undo framework.
No benefit for tool classes to inherit from QObject
setFrameImage supports frame replacement, in addition to frame compositing
Inline matrix-mapping functions
Separate overlay-drawing routine out of refreshPixmap.

Still glitchy outside of m_pEditImage on view transform.
Set document's isModified flag on frame translation operation
Separate overlay-drawing routine out of refreshPixmap.
Change calculation of visible frame upon resizeEvent.
Further differentiate scene modification signals.
Use Java-style iterator, and invert layer sequence on drawing.
Bucket fill on view translation.

A bit slower, but removes artifacts when panning.
Enable building in both release and debug mode in parallel.