Refactor UI

#### HTML

* Use HTML5 elements such as `header`, `article`, and `footer` where appropriate.
* Restructure into modules with header, body, and footer components.
* Add a 12 column grid

#### CSS

* Split into separate partials based on SMACSS: base, layout, and modules.
* Use BEM syntax throughout.

#### JS

* Create a **lightbox** singleton, which binds to clicks on elements with a `data-lightbox-img` attribute, and opens the referenced image in a lightbox. Includes `open`, `close`, and `setContent` public methods.
* Add a **ReadMoreWidget** class which adds the toggle button afer the expandable content. Create a new instance for each `.read-more-container` by default. Includes `expand` and `contract` public methods
* Concatenate files into `all.js` using `guard-concat`
* Move JS to bottom of body element