Make input test window available via app
brushmanager: assorted code tidying
Various debug prints: replace w/ standard logging

Python has a standard logging module with lots of goodies. Categorization
of messages and module reporting to name just two. Let's start using it in
place of print (or print(), considering Python 3).
Merge branch 'mypaint-head', update to new logger

Conflicts:
	lib/document.py