A number of fixes following testing of recent changes:
- PROCinsert_gate: Ensure pointers to music data are preserved when the Gate heap block is resized, to prevent possible corruption
- PROCmove_note: Call to PROCSetupBarStarts is superfluous here, since it's called later on
- PROCplay_notes: Fix calculation of tie lengths
- PROCdraw_notes: Ensure dots are positioned correctly after staggered notes
- A number of Maestro files I've come across have key signatures of 1/x. Not sure how, since AFAIK the interface has never allowed it, but since such signatures are technically legal, add sprites to display them correctly when encountered. Also extend the interface to allow them to be entered into scores. These bar lengths seem to cause the scrolling to become a little jerky (not sure why) but otherwise appear to work fine.