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.
13px is way too small, if anything it should be bigger
fix bug with new buffers and notify level
Fix bug with onlyUnread and buffer with notifications without unread
messages
New plugin: spotify
plugins: add SoundCloud and MixCloud support