Charter: please review!

I have updated the proposed recharter from our conversation at the face to
face meeting: please take a look at
https://w3c.github.io/immersive-web-wg-charter/immersive-web-wg-charter.html
and let
me know what you think; comment here or file issues on the charter repo
<https://github.com/w3c/immersive-web-wg-charter/issues>.

Comments from the commit
<https://github.com/w3c/immersive-web-wg-charter/commit/d1c0f08b7586b99724c1979ffe510307062ffbca>
:

added "Potential Normative Specifications":
Access to Raw Camera FramesImage Detection
Face Detection
Depth/Occlusion APIGaze tracking (Diane)
Navigation

Stated all specs are still expected to be incubated.

Stated in RWG that it may turn into multiple deliverables.

Changed wording in Anchors - "in the world" -> "in local coordinate systems"

Anchors only inside a session, not across sessions.

Remove list of "such as..." devices.

Put in estimates for completion dates.