Removing Staves: yStart, staffSections, and full removal.

1) RemoveStaves now return 2 more objects:
1.1) yStart: A vector containing the positions of each staff line in the
Y axis. Each section has 5 staff lines.
1.2) staffSections: Number (scalar) of sections to represent a block
(i.e. it should be 2 in Jingle Bills and 1 in both Bach's and Twinkle
Twinkle).

2) Found a solution to fix the un-removed staff line parts in some cases
(e.g. Twinkle Twinkle).