Add serialization mixin
Merge branch 'master' into load
Save track sequence as a file on the server

This is a start towards being able to save/load tracks for user accounts
but for now it is motivated by having a nonblank composition for demo
purposes
Demo track that's loaded automatically
Add spec for save/load, minor improvements other
Get loading of demo track working
Get scale selection working again

There are definitely bugs here. In particular, the too many oscillator
problem shows up after changing the scale again and again.
Merge branch 'master' of github.com:alexholt/toneblaster