[SDL 0273] WebEngine Projection mode

[theresalech]

Proposal: WebEngine Projection mode

This proposal is created based on discussion in smartdevicelink/sdl_evolution#767.
It extends SDl-0240 - WebEngine support for SDL JavaScript to allow using the WebEngine app's web view for the HMI in addition to the other available SDL templates.

Review: smartdevicelink/sdl_evolution#912

Steering Committee Decision:

The Steering Committee voted to accept this proposal with the revisions outlined in this comment.

The proposal .md file was updated to reflect these revisions on 6/8/2020.

[theresalech]

We've determined changes to the server are not needed to implement this feature. API documentation was updated in PR #193.