Improvements in RPC transport layer

[Starzu]

Description

There are a lot of problems with the Atmosphere library. Eg. SSE problems, JS client is hard to debug - one file ~3.5k LOC...

TODO

• Consider which way is the best:
  • improvements in the Atmosphere codebase (with a scala.js implementation of the client?)
  • switch to another library
  • write a custom RPC transport layer
• Requirements:
  • reliable client id tracking - unique id for an opened application (browser card)
  • WebSocket as the default transport mechanism (and a fallback method - probably SSE?)
  • an automatic reconnection in client
  • information for the application about lost connection
  • server: sending a message to the selected client or broadcasting

[mereszeta]

Issue with current usage of atmosphere: #394