Guitar Pro feature updates

## New edits since PR #1101
- Confusion between brush and arpeggio sorted out - swapped those around;
- Bravura glyphnames reverted - font left untouched;
- Drawing and boxing of free time revamped, now survives spatium changes;
- Fixed key signature warnings;
- Ottava support improvements;
- Updated layout for fingering;
- Bugfix to centering of empty bars in some Guitar Pro versions.

## Previous description of PR
Latest feature additions to Guitar Pro imports. I've nothing on backlog so should be able to get back to smaller PRs after this...

Changes outside of guitar pro implementations include:

- New symbols to fonts (volume swell, large parenthesis, 4 kinds of "vibrato" markings).
- Chordline length now editable and displayed in palette for Guitar users.
- The concept of a drumset 'kind'.
- Tremolo bar implementation edited slightly.
- Time signatures now have a _freeTime property, when this property is set to true parentheses are drawn around the time signature.
- Equality operator defined on pitch values.

Any questions/issues, feel free to comment!

Looks like it might be there to force the removal of CDATA pseudo-"markup". I'll check though.