Refactoring

Moving things around
Added setup.py and __init__.py
Made signal/model wrappers actionable

Added common wrapper ancestor Actionable, which handles instance
specific actions.
Added toolbar actions' icons

See attributions.txt for source of some icons.
Introduced threaded processing

Made an utility class for processing in a separate thread. This is
desirable, as then the main GUI thread is freed for processing the event
loop. In other words, it keeps the application from becoming
unresponsive. A progress bar pops up, which can either just show "busy"
state, or percentage of completion. Some care should be taken when
processing in a separate thread, as drawing is only allowed on the main
thread. If needed, this should be handled by events.