Grid refactor and feature lock

***The time is now.***

After a lot of internal debate, we've arrived at our final set of class names for the grid. Of course, these are just our presentational classes, more oriented towards rapid prototyping. With this grid moreso than the Foundation 5 grid, we *really* encourage folks talking this code to production to consider using mixins again. This grid can get heavy on classes due to its flexibility.

The components are:
 - [x] **Frame** (`grid-frame`) – a wrapper for your whole app that constrains the grid to the browser's viewport.
 - [x] **Block** (`grid-block`) – your catch-all grid element for just about everything.
 - [x] **Content block** (`grid-content`) – your non-flex element for housing regular content.
 - [x] **Container** (`grid-container`) – a horizontally-centered block element with a maximum width. Meant for more "normal" layouts, or constraining and centering the content of a grid block.

The grid code also needs to be refactored in these ways:
 - [x] The panel reset styles are hefty, so they should be moved into a `.panel.block` selector, so they're only brought into the code when a block also is a panel. Right now the panel resetting styles are used on blocks all the time, even if the block isn't a panel.
 - [x] The block grid code needs to be made into a mixin, as it's currently just raw CSS. The mixin will probably be called `grid-layout()`.
 - [x] Content blocks won't have padding by default, to make nesting new grids inside content blocks less of a hassle. Instead we'll add a `padding` class for use with the block classes.
 - [x] The default behavior of grids will be to stretch their children and not wrap. To trigger wrapping functionality, a `wrap` (or maybe some other name) class should be added. Block grids will wrap by default, obv.

And *lastly*, we get to refactor the existing docs to use these new classes!
 - [x] Refactor all the things