Add simpler Bootstrap theme support

Remove all custom variables and color definitions, replace with
Boostrap-only variables.

Conflicts:
	_stylesheets/page.css
	_stylesheets/page.scss
Add to-be-used Bootstrap external theme
Switch theme back to default Bootstrap out-of-box
Add YAML field for custom theme support
Merge pull request #1 from jordanmccullough/theme-support

Theme support