Allow revising time axes to measure # through using tempo input

[wustep]

Might be tough given the data manipulation, but I think this is super key for utility

[jrg94]

This is doable, but would require quite a bit of preprocessing as tempo can change. Data representation can handle it though. Append measure number (plus length) to each sample.

[jrg94]

May also need to account for time signature (3/4, 4/4, etc.).