Moved Kegs to a plugin and added tooltips.

I figured adding them to tanks is much easier through events, while,
even though it builds the names and adds them right before they're
needed, I can't easily add an itemblock class for tanks to use to add
tooltips.

Also added tooltips for potion ingredients, and some other little cool
things, tool-tip wise.

Moved Kegs to a plugin, and am thinking about moving the Brewery and
Sprayer into their own machine plugin. . .