Add conveyor speed settings to phone app

[VanceVagell]

Currently, when you build a SMARTA you need to manually edit the Arduino source code to adjust timing values for the conveyor belt, to ensure it dispenses 1 piece of food at a time, then rewinds properly for 1 cup and 7 cups.

Instead, those settings should be part of the phone app, and sent to the Arduino with each dispense/rewind/full rewind command.

This enhancement request is to add settings for these 3 things:

1. Dispense speed
2. Rewind speed
3. Full rewind speed (go back 7 cups)

And the Arduino app should use the passed-in values rather than the current constants.

[VanceVagell]

Actually, it seems the "full rewind" isn't used at all anymore. So just need settings for dispense and rewind (and the Android apps smartly send the correct number of rewind commands to Arduino, depending on how many dispenses have happened).