Tony: a tool for melody transcription

Notes can be edited in multitool mode with 4 different handles:
top -- note drag
bottom -- note split (or delete, if used with shift)
right -- move right border
left -- move left border

Firstly, the left and right handles are not visible. They need to be visible, and BIG, so that people find it easy to perform the onset/offset shifts.

Secondly, since we provide an annotation program, there's currently no good reason to move notes, so I think we should de-clutter the multi-tool by removing the vertical drag function. That would give us an easier handle visualisation, too.