Work index design

Refined the design of the Work index page to so that all project summaries lay out in a single column. Removed image floats on large screens to allow each project image more breathing room, maintain a better visual rhythm as users scroll, and create a more consistently positioned call to action for each project. This layout also creates more visual consistency between the Work index page and individual Project pages.

TODO:
* Replace current large size thumbnail assets to take advantage of additional available width, while also cropping heights to allow each project to fit within reasonable vertical viewport sizes.

Closes #11.