make mouse range mode do something interesting when in internal/note edit mode. not...

make mouse range mode do something interesting when in internal/note edit mode. not entirely finished because the usual modifiers to add/extend the selection don't work correctly. note that this works both on the scroomer (where the modifiers do work correctly) and in the track (where they do not)

git-svn-id: svn://localhost/ardour2/branches/3.0@11273 d708f5d6-7413-0410-9779-e7cbd77b26cf