Use the WebAudio API for more of the heavy lifting

[veltman]

The earliest Audiogram prototype used the WebAudio API to get the waveform data, and we still use it for the summary version in the editor. But we ran into a lot of inconsistencies with decoding and duration detection. If we can get that working properly, we would reduce the server-side complexity and be able to drop the libgroove and node-waveform dependencies.

[veltman]

Anecdotally, libgroove dependencies seem to the sticking point for a lot of local installations. It would be great to ditch them.