More progress toward subanalysis

More progress toward subanalysis
With our previous efforts at turnning Sequence into a string, the
places where we were comparing a Sequence to a string didn't work so well.
So this patch lets the compiler cast strings and const char *s to Sequence.

additionally I made the copySelectedTrackAs functions a bit more generic
by making the base function copySelectedTracks a template function
that returns a list of formatted objects. The two string style copy
functions AsFasta and AsString, then needed a bit more code to convert
the list back into a string. But I needed this so I can let users
edit what regions they want for SubanalysisWindows.

And lastly, there's a very simple box for defining a subanalysis that
still needs to be connected to the above copy functions.