Updates to BEM Naming Conventions

Changes the class names found in styleguide.css to use BEM naming
conventions as outlined at
http://csswizardry.com/2013/01/mindbemding-getting-your-head-round-bem-syntax.

Updates block.inc.php to use new class names.

Modifies whitespace in layout.css to comply with the other files in
the project.

Updates buttons.css to follow BEM naming conventions.
Adds reference ids to styleguide block

A styleguide block is now given an id of r . $section->getReference().
For example, styleguide block with a reference of 1.2.2 would have an
id of r1.2.2 (id's cannot start with a number).

This allows direct linking to a specific reference in the styleguide.