Desktop friendly command events

[cblgh]

This PR makes all slash commands' info event also include which command triggered the event. As a consequence, handling command output in react-style apps like cabal-desktop should be a lot easier and less haphazard.

CabalDetails._res has been converted from being an object, returning three functions (info, error, end), to a function. The function takes the command type as an argument, and calling it returns the same object as previously—the key difference being that the three functions have had their payload annotated to include the command type.

(n.b. This is not entirely correct, as only info has been annotated to include the command key,)

The emitted command event has also been removed, as it was unused in most places I can see cabal-client being used (I checked desktop, cli & timgoeller's bot framework).

@nikolaiwarner @khubo lmk if this doesn't make sense (i think it should tho?)

[cblgh]

cc @nikolaiwarner @khubo @substack any thoughts on the above? let me know where things are unclear and i'll write comments + docs to clarify 🖤

basically: client commands now emit:

• which command caused event info to stream (channels, names, whisper etc)
• a unique id (string), identifying the same event stream across many different events.
  this might be useful if you have many event streams at the same time of the same type? might be superfluous.
• a sequence number, keeps track of the order of events.
  sometimes the first emitted event contains a special message—e.g. the /channels command that has a header info message and then emits all channels in subsequent messages
• an end event, signifying the end of info stream
  (this fixes a bug in cabal-cli , where /clear would only be updated if some other type of event (e.g. peer connection) was triggered after a clear had been issued—bug probably surfaced by this commit)

i encapsulated the extra data in the meta key of the emitted object, primarily to prevent future collisions if we add / tweak emitted event data. let me know if i should collapse the contents of meta back to the original object

so

> /channels 
[...]
this.cabal.on("info", msg => {
  const meta = msg.meta
  // meta consists of: meta.uid, meta.command, meta.seq
  console.log(meta)
  // => { uid: '1613387148891', command: 'channels', seq: 23 }
})