Add source select to gate/comp side-chain

Small improvement:
Add source select (any socket) for gate and/or compressor side-chain.

Use-Case:
Useful for Tom gate triggers, which simply need an empty socket with some gain.
Not sure how useful for compressors, but might as well…

Minor critique:
Block Diagrams start on Pg. 108 Section 18 of the V1.50 SQ Reference Guide
It would be a good idea to add the source capabilities of the side-chain filters somewhere.
FYI, they are currently: Self, 1-48,Buss (Aux/Grp/Mains/MTX)

Searched forums, didn’t see a similar thread to +1.