Get rid of xmpp.jid()

[cburschka]

#292 tried to solve a very real problem - all kinds of code was expecting a room/nick, and couldn't handle different kinds of JID.

For some reason, the solution was to make such code accept an object with various keys. That object would then be turned into a JID according to complex and hard to explain rules.

This led to code having to pass undefined to get the current room broadcast address, {} to get the domain, {room: null} to get the MUC domain, and {jid: '..'} to pass through a JID directly.

The sane way, I now realize, is to simply make all functions expect a JID. domain values can be taken directly from the configuration, a jid can be passed directly, and the only thing remaining is a function that turns a roomnick into a JID.

  /**
   * Generate a JID from a roomnick.
   *
   * @param {string} room (defaults to current room)
   * @param {string} nick (leave empty for groupchat)
   *
   */
  jidFromRoomNick: function({room, nick}={}) {
    return new this.JID({
      domain: config.xmpp.mucService,
      node: room || this.room.current,
      resource: nick
    });
  },

[cburschka]

Ironically, the function actually used to be called jidFromRoomNick.

The sole problem was that it took positional arguments - and, of course, that it was called by .pres/.msg/ instead of their callers.