Issue 1266: Dots in chords can not be moved

[Seafire]

This issue bothers me, so I took a look at it.

It appears that extremal_head_ of the Dot_position struct found in dot-configuration.hh/.cc and dot-column.cc exists solely to limit the Dots #'direction setting to the main note head. I removed this limitation and it fixed Issue 1266. I've run a few dotting tests and I didn't find any issues with doing this. Still, why was this limitation put in place and can it be removed? Git didn't tell me.

Justin