Need to be able to configure a reality before it is shown

[blairmacintyre]

Does reality.connectEvent only get triggered when a new reality is activated and connects? If so, that means that reality is visible already when we have a chance to configure it (e.g., the panorama demo doesn't configure the panorama-reality till it connects).

Four things would be useful here:

• knowing if your "requested" reality is going to be shown. We aren't going to guarantee it, but feedback to apps would be useful. A promise that returns "yes, we're going to show it; no, we're not going to show it yet" would be super useful. Perhaps another event on that reality that can say "reality activated" or "reality deactivated" if/when it gets swapped in/out later.
• When a reality is requested or installed, perhaps we can pass parameters to it. The panorama could pass an initial panorama; streetview an initial location if one is known that's different than the "Current location", or flags saying "current Argon4 reality location" or "current physical location", etc.
• When a reality is installed, we should get some sort of handle or promise that gives us a connection to it before we present. If reality.connectEvent does this already, great.
• We should consider having a reality.ready or similar event that a reality could trigger when it's "ready to show". Some realities may just trigger this immediately, but a panorama reality (for example) could wait for the initial panorama to load

We should probably also update the realities to show something like an "initializing!" screen until they are in a known initial state, to get rid of the ugly partially loaded states we get now.

[blairmacintyre]

reality.connectEvent happens only if a reality has custom protocols.

But, yes, we need a reality.ready concept