system: NodeProxy2, allow choosing arbitrary server node position
system: NodeProxy2: allow setting name, reflected in SynthDef name

Moreover, make PatchEnvironment set NodeProxy2 name to environment
variable name.
system: improve allocation of SynthDef names

NodeProxy2: if own name is set, use it exclusively for SynthDef name
PatchEnvironment: set proxy name to key + environment object's hash.
system: NodeProxy2: improve playing SynthDef names (keep to minimum)
system: PatchEnvironment: be human-friendly: use key alone as proxy name
system: NodeProxy2: fix case when source is target but not running
system: NodeProxy2: implement selective mapping to source bus channels
add preprocessing.scd: actual sensor preprocessing setup

* Separate preprocessing into several nodes for easy mapping.
* Run all nodes in a dedicated server group.
system: NodeProxy2: add 'silence' method to remove public playing synth