Add bitly url shortening

Add excludes lists for bitly shortener. Only shorten longer urls.

Make sure config values are set.
Add goodbye plugin
Fix help command with unknown commands
Seen command implemented. Tracks when users are active in the channel.

Goodbye Plugin improvements.
Reconnect if connection lost
Fix seen reply if bot hasn't seen the user.

Move Users class to seen plugin.

Fix !seen case sensitivity. Update users command doc string
Fix seen command message
Merge branch 'chances-fixes'