Fixes probability bug and game mode bugs

Probability was set to 50% instead of 20% for the attack game mode.

Game modes were carrying over to the next game.
Update UnoBot.java

Set probability for attack mode to 20%
Merge pull request #10 from MikeOntry/patch-3

Fixes probability bug and game mode bugs (pull request from MikeOntry)
!leave and !endgame fixes

The !leave command did not work properly for me. When a player left during their turn the game would still freeze up. If they joined back and left again it would let the game continue. This is fixed now.

When a player leaves on their turn it will properly remove the player and switch the turn to the next player and display the "TELL USER TO GO" information.

Also when playing with the AI I noticed it did not leave the channel after using the !endgame command. Now it will.
!uno command timer and !endgame fix

Sets a 5 minute timer on the !uno command. If the !deal command is not used after 5 minutes it will automatically !endgame.

Also I noticed if you try to use the !endgame command before you use the !deal command it didn't work. Now it does!
Merge pull request #11 from MikeOntry/patch-4

!leave and !endgame fixes
Merge pull request #12 from hoerup/master

Handling of nick should be done outside UnoBot class