cleanup
removed ModifyPart/changePart. Replaced with ModifyPartLength etc.
typo
assertions for UndoOp ctors
removed unused UndoOp ctors
removing commented out code
Parts have their own, non-shared EventList (still WIP!)
removed refcounting in Eventlist
Part::events() is now a const EventList&
chaining parts now a Part:: member function
made Track::events, ::mpevents public instead of using an insane reference-accessor
TODO: need a grouping indicator of clones (like the eventlist pointer was used for)
some constness
some const-correctness. Part interface overhaul.
various fixes.
clean disabled code in midiseq
tiny fix
cast away constness in authorized audio-thread-code: doUndo etc
Event/Part selection now via UndoOp::Select*

additionally:
added Song::applyOperation()
removed unused param from (un)chainTrackParts
cleaned up misleading orphaned code in MidiSeq::processMsg
removed unused seq/audio-messages. more orphans
fixed PartCanvas::drawMidiParts
MidiTransform now uses operation groups
fixed insane ModifyEvent old/new twist
more applyOperation. MusE compiles again, still does not link
more const-correctness for Part*