Renamble client names / Pretty Names (Saved in the session)

[diovudau]

This depends on #32 for saving additional data.

Proposal to let the user give names in the NSM GUI, to rename individual instances to keep them apart or rename them according to a role: I usually name my instrument-programs like Carla or Zyn "Melody", "Bass" etc.

This cannot be implemented by existing mechanisms: Clients can specificy their own name on announce, which are used to save the session.nsm so they cannot change (see API docs). Clients can give themselves a label. These are deleted when the client stops, or the session is closed. And they are already used for other purposes (for example Fluajho reports the loaded soundfont name via label).

Argodejo implemented this as a proof of concept through the non-music client "nsm-data" (together with session notes)
On the one hand this already works and prevents further complexity in the daemon, on the other hand this creates overhead both in broadcast messages, in the GUI and the mere existence of the speciality-client.

And for clients without NSM support this will never work on the client side.