sound improvements

Mostly, compute overall energy internally in each node, to allow
parameter customization.
preprocessing: no use for 'busy' anymore
system: NodeProxy2: separate control mapping and setting
system: NodeProxy2: fix mapping validity logic
system: NodeProxy2: support setting several controls at once
adapt performance code to system changes
gui: ProxyGui: improve controls

* Let controls be an array of associationg instead of a dictionary, to
  preserve order.

* Fix initial knob value: use spec to unmap proxy value.
sound: add controls to all node definitions
system: prototype BufferPool, BufferPoolSelector
system: ProxyGui: support buffer selection
system: improve gui classes
system: BufferPoolSelector: accept choice on double-click
system: ProxyGui: small cosmetic enhancements
sound: add all controls for buffers
main: add second MiniBee, improve GUI
system, gui: volume control in dB
sound: grain_reveal: raise grain amplitude
system: PatchEnvironment: prepend own name to node names
activate MiniBee pressure sensor again
main: gui: make explicit proxy order