New Guitar Pro feature support

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!