Reevaluate Julia->browser requests

[twavv]

A while ago I added the ability to send a request from Julia to the browser and expect a response. This doesn't really make sense because we assume that there may be many frontends connected.

We should either wait for all connections to respond and return an array of responses or take the first (this should be configurable and maybe default to throwing an error if more than one client is connected).

Or just remove these kinds of requests altogether (that does remove the ability to issue evaljs commands, but that's already supported in Blink and is impossible in Jupyter). We'd only lose the functionality for Mux essentially. But we should probably do the first one.

[shashi]

So you're sending these messages to a "scope" right? That's not impossible in Jupyter?

[shashi]

evaljs takes scope as an argument and gives you the scope JS object in scope variable or this (i don't remember which one).

[twavv]

You can send messages to Jupyter you just can't block while you wait for a response.