Make dev-only updates (to index.html and Makefile)

Add viewport initial scale and box headings to index.html.
Update Makefile to utilize new tools (serve.js, karma-cli).
Remove old, unused files and styles

Replace xlarge box size with large, remove xsmall size, and delete
unused Highcharts-related sass files.
Add some variables, fix various dimensions, move selectors

All paragraphs should have line height 1.5, but everything else should
not. Only primary box descriptive texts should be grey.
Add some variables, fix various margins and font sizes.
Split fun-fact-box into fun-fact-box and breaking-box

Boxes can be fun-fact-boxes without breaking page flow, and thus the
flow-breaking styles have been moved to the breaking-box class.
Adjust box dimensions and increase size of action buttons when on mobile

On mobile devices, boxes should take the entire width of the screen
but only use as much height as they need. Action buttons should be larger
and more thumb-friendly.
Merge pull request #8 from bdo-labs/responsive-mobile

Fix some dimensions all-around and add responsiveness to mobile devices