plugins: (youtube) make video preview slicker
plugins: (image) support fukung.net

Links to http://fukung.net/v/foobar.gif end by the actual image
extensions, but the full image path is under
http://media.fukung.net/imgs/foobar.gif.

This commit replace the URL prefix if it matches fukung.net/v/.
Handle wrong password. Fixes #4.

This commit introduces a way to handle wrong password.

The only way to know it is by sending an other message after the init
one.
If we receive an answer to this second message id then we know we are
connected with the good password, otherwise we will received an onclose
event from the websocket.
plugins: add SoundCloud and MixCloud support