first frame now always has cel
Merge branch 'master' into multi-layer

Conflicts:
	lib/animation.py

	modified:   gui/animationwindow.py
	modified:   lib/anicommand.py
	modified:   lib/anilayers.py
	modified:   lib/animation.py
	modified:   lib/document.py
	modified:   lib/framelist.py
mypaint layer names now automatically managed
fix error on remove last layer