Move <main> and .sidebar markup out of PHP

Add more efficient LESS with variables

Add new line to _variables.less

Add sidebar class to body element instead of main element

Change body sidebar class to .sidebar-active

Change body sidebar class to .sidebar-primary

Correct spacing issues
Merge pull request #1090 from CFXd/move-main-and-sidebar-markup-out-of-php

Move <main> and .sidebar markup out of PHP and into LESS