Add new states 'loaded', 'connect' and 'fatal':
- Loaded state is first page state. Pass WebSockets mode message using
  this state.
- Connect indicates that the user has issued a "connect" but we
  haven't gotten an WebSockets onopen yet.
- Fatal is a condition that indicates inability to continue on: right
  now, lack of WebSockets/Flash or non-working canvas.

Move much of the actual state transition code into updateState.

Handle 'password' state better in default_controls.js; instead of
disconnecting, prompt for password to send.

Add comments to updateState indicating possible states.