Base structure for WAMP messages processing and Tornado-related handler

Added features:
- WAMP `tornado WebSocket handler`
- `Extendible message` pattern for parsing and creating WAMP messages. It is currently applied to: `HELLO`, `WELCOME`, `ABORT` and `ERROR`
- Extendible `processor pattern`, which can be easily coupled to the WAMP requests handler. The handler delegate messages to specific classes, which are responsible for processing and defining outcomes. It is currently applied to: `HELLO` and `UNHANDLED`.

Regarding tests: 99% coverage
@fredrikbonander I'm working on this right now - but in our internal project (ShinyWallhack), which extends TornWAMP. Basically, nor WAMP nor WebSocket protocols define any restrictions for someone opening multiple "connections". The concept of "user" and the restriction of only having a connection by user is internal to EF.