Support passing IParty identity id

[sevenbitbyte]

Allow changing the party identity's id. It's currently hard coded to primary which isn't very helpful. Maybe make this a fully fledged url where host & path point to the cloud location of the party or webapp. The user field could be used to stuff user/key id numbers.

dataparty-api/src/party/iparty.js

Line 222 in 62e3171

this._identity = new dataparty_crypto.Identity({id: 'primary'})