styles.less: Add primary and bold colors

Add extra colors for theme. Derived from:

http://colorschemedesigner.com/#3p31Tq.Nhw0w0
Sub-divide Less files

The idea here is that CSS rules can be divided into files logically and
then combined into the site stylesheet at compile time by using the
@import Less CSS directive.
Add 'make clean' target
git: Ignore generated CSS file
Further CSS sketching