Persistent Server Identity

[bangnoise]

Generally applications use a combination of app and server name (if present) when maintaining clients through server lifetimes or reinstating Syphon state from saved files.

One situation in which this is inadequate is when server state is stored in a file opened by different applications, as the app name will change, making client restoration impossible based on the app/server name combination.

Having a persistent unique identifier for servers would

1. Allow clients to reconnect to servers even when the servers are restored by different applications.
2. Allow a server which has a fixed meaning in its application to be renamed but preserve client connections (e.g. the server on a host's Layer 1 is renamed from "Stars" to "Unicorns" but client connections preserved in files would remain).
3. Make saving and restoring Syphon state for servers and clients in documents much simpler.

This was previously discussed and largely rejected in #23 in the context of SyphonClient persistence.