Wait Interface

[benbjohnson]

Add the ability for the external language to know if the UI is waiting for some reason.

Requirements:

• Wait interface should check a boolean called Melomel.busy.
• UI should wait for at least 5 frames in between calls.
• UI should check if a busy cursor is visible.
• UI should allow for application to manually set Melomel.setBusy().

[benbjohnson]

Implemented everything except for Melomel.setBusy(). Will add it if requested in the future.