[musicxml] [tablature] and the up-bow and down-bow tags

A guitar/banjo/mandolin... strum is a fundamental part of tablature that is marked with an up or down arrow beside the chord in the staff. MusicXML uses the [up-bow] and [down-bow] tags to denote strums. It also uses these tags for bowed instrument directions. These markings sort of look like 'V' and 'n' above the staff.

Two problems in Musescore 2.0 beta 1.

1. The MusicXML importer needs to (some how) distinguish bowed and plucked instruments at load time and mark the bowing/strumming appropriately. Today you get a whole lot of violin bowing marks above the staff in guitar tab. I guess the program needs to look at the midi instrument and figure it out from there.

2. The bowing marks are drawn right on top of the chords. So if you see an 'Am' with a 'V' drawn on top of it, up strum an 'Am' chord.

A quick fix would be to never draw bowed instrument markings in plucked instrument tab. A better solution would be to draw the appropriate 'strum' arrows in the tab for plucked instruments. Another solution would be to leave it alone and fix the chord/bowing text drawing collisions.