Creating a first minimal viable feature of pair programming with Che-Atom teletype

[sunix]

MVF to join an existing Atom Teletype portal from Che (as a guest portal).
Final result should end up with a PR in Che6.

• spike Spike POC pair programming feature with teletype and/or ot.js #438
• remove hard coded value, set values from Preferences panel (20)
• package teletype-client for browser (20)
• clean up, concider using jsinterop instead of overlays (25)
• create a new project type "remote teletype project", shown in project explorer (50)
• simplify login flow, user shouldn't go through https://teletype.atom.io/login (30)

[slemeur]

Linking to eclipse-che/che#8286

[garagatyi]

Since this issue is for other teams I believe that we can close it in our repo. Feel free to reopen if you think otherwise.