WIP-MEI: Fixed: safePitch() Accepts None as "accidental" kwarg

Giving None or '' as the "accidental" kwarg to Pitch.__init__() would raise an
error. We avoid this now.
WIP-MEI: New: Enormously Hacked-together Strategy for Slurs and Ties

It's ugly and inefficient, but it works. And "working" is the first of
many steps on the pathway to glory.