Bend Tool: Apply bend note-to-note and other improvements

Apart from the bug-fixes documented at Bend tool: notation and layout problems (and see forum thread Request for bend symbol features ).

1. Apply button: Currently missing.

2. Note-by-note application: AFAIK, in practice, bends always extend from one note in a score to the next note. But currently, the bend tool applies bends on a space-by-space basis which can make it tricky to use.

My request is to change this so that each grey segment in the bend-tool window refers, instead, to a note-to-note section of the bend, rather than a space unit (sp.). So, a bend which is 2 segments long (in the bend tool) will extend for 2 notes in the score; a 3-segment bend will extend for 3 notes in the score and so on.

(Space units should be an alternative option for those who want it, and to ensure back compatibility.)

3. Optional Prebends: Currently if the first point of the bend (in the bend tool) is greater than zero, the program adds a prebend. However, this should be optional. If unticked, an initial value greater than zero would allow the user to start with a down-bend instead.