Replaced semantic.gs with Jeet's grid

Sorry this took so long. :laughing: 

It's rather late here so I'll be writing the docs in the morning - for now the comments I added should do well as reference.

While adding it in though, I had this very strong bubbling opinion that the code should be refactored a little bit to make use of some internal functions that would help make it more readable. So I'll work on that too at some stage, but for now - the grid's here, it works, and the `edit()` mixin is super awesome. Not sure how well it'll play with the current livereload implementation, but it looks magnifitastic while developing with strategies that only reload the CSS.