Buffer and command improvements

Created by: ca1ek

1. Leaving and joining messages go to the buffer instead of showing up for all channels even if you weren't looking at them
2. Redesigned the buffer so it stores messages and other as objects, not plain text.
3. Fixed an error that made chat messages not print after switching with a /goto
4. Added short forms of join and part commands, /j and /p
5. Added a short form of goto command, /<channel_number>