Less brittle mapping to midi-notes.
Don't depending on the name of the sample once downloaded to disk map. Explicitly map freesound ids to the notes.
Use Freesound sample which preserves the freesound id.
libs -> samples
freesound-sample takes an id not a path.
Merge pull request #233 from josephwilk/less-brittle-piano-samples

Less brittle mapping to midi-notes.