Refactor sugars into a module instead of a magical load-time thing

This commit moves the sugars into a "Sugarable" mixin that defines a `node` object and wires all the pieces together for a DSL to include Chef Sugar. Individual classes can then `include Sugarable` and they get the DSL.

This commit eliminates the nasty load-time stuff that I did originally.

/cc @opscode/release-engineers @danielsdeleo @sersut