Add layout UI helper documentation

[kadamwhite]

This PR represents @Wilto's work implementing a documentation page for the ui-layout helpers, and also contains some overall docs improvements such as indicating the active class in the navigation (not yet styled).

Run the docs server at localhost:4000 with the command grunt docs.

This PR

• Merges in layout utility class documentation
• Properly documents all development tasks and commands in the README
• Synchronizes the information in the README with the public-facing docs site content, including replacing outdated material from the prior version of this repository
• Fleshes out the demos in the ui-helpers page with descriptive copy

[mzgoddard]

Gave everything a read. I'm not good at copy editing but from the tech side it looks good.

[mzgoddard]

:shipit:

[mzgoddard]

🚀