use Qt Signals & Slots for progress tracking

use Qt Signals & Slots for progress tracking
this replaces my first attempt that used boost signals (which is now
removed from the repository).

Mussa and NwayPaths now inherit from QObject and can emit a progress
signal to give some indication of how far they've gotten at long running
tasks. Though I don't have a solution for long running seqcomps yet.

Also instead of hard coding a % constant to cut down on the number of calls
to emit the signal, I should use some kind of timer.