Big refactor, closes #38, closes #37, closes #32, closes #31, closes #21

All root folders are now variable. There is now a central config for
both Grunt and Assemble in the root (config.yaml) and one especially
for Assemble (site.yaml).

The Grunt folder is now prefixed with a dot by default, as is the temp
folder. Other than that everything has been slimmed down and
modularized as much as possible.