Fingering improvements

See http://musescore.org/en/node/36846 for discussion.  There have been a number of threads on these issues over the past couple of months leading up to this as well.  What I have here may or not turn out to be the definitive answer, but I think it's in a very good state.

Unfortunately, vtests don't make sense for the changes to the automatic positioning algorithm since the results are applied as "user" offsets and "baked in" to the score file.  That's not my doing; it was that way already.  It would presumably be possible to change this to work more like other automatic positioning, but I'm not so sure that's actually a good idea in this case.  Positioning for fingerings is much more subjective and situation dependent than for the other things we place automatically, such that it's still quite likely one will wish to override the default placement no matter how hard we try to do it well.  And in overriding the defaults, it may be more straightforward if "0" user offset is a always a predictable starting point.

Anyhow, a change to how we *apply* the automatic positioning once calculated could be done at any time before or after my changes to the algorithm itself - the code is well enough separated out for that.