Clowncart tweaks & code improvements

Created by: unid15

-Fixed https://github.com/d3athrow/vgstation13/issues/2883

-Allows feeding the clowncart anything that contains banana juice (amount of fuel added = amount of banana * modifier(50), upgrading the clowncart will increase the modifier to 70 and 80) -Allows using plant bags to dump shit into the clowncart -Traitor peel banana cost upped to 8 (was 2 before, compared to normal peel's 4) -Upgrading the clowncart now notifies you when features unlock -Examining the clowncart will show you its current mode -Banana peels no longer give banana juice but heal twice as much (10 instead of 5 woo)

-Code now uses defines