Multiple banks per instrument

This (very big) patch enables to have multiple banks per instrument.

Instruments can now have multiple banks like Direct, Overhead for example.
In Hydrogen, it acts as an additional layer between Instruments and Layers.
Instruments can have multiple Components, and each Component multiple Layers.

Components (or banks) are as well centralized at the Drumkit/Song level.
For every bank an additional mixer strip is created, so user can quickly change the volume for a specific bank (for example Overhead) on all the instruments.