Allow to reconnect client into the room

[endel]

When the WebSocket connection drops unexpectedly, it should be possible to reconnect that client within a certain timespan, even if the room is locked.

Scenarios:

• User closed browser tab accidentaly (colyseus forum)
• Mobile device went to sleep mode (locked) (defold forum)
• Switching from Wi-Fi networks. (Keep user state upon reconnection #8)
• ...any unexpected action that closes the WebSocket connection. (Losing connection to room on unstable connection #68)

[endel]

Hey @dossy @sandrosc @AnubisCode @ruifly2012,

I'd appreciate if you all could vote on the poll at the pull request #154

Cheers!

[dossy]

I voted in favor of on-by-default, although that breaks backwards compatibility in case anyone implemented their own reconnection mechanism in their own codebase, but ultimately for future developers, I think the on-by-default will be the useful behavior.