Fixed header logo

Removed the st_header function from the header.php file. This function
generates all of the header markup, including placing the nav menu
below the logo, and does not include the search bar - therefore I'm
just using custom HTML markup that follows the Skeleton theme's basic
structure

Added logo markup to header.php file (taken from functions.php and
slightly modified)

Re-added role="navigation" to nav container (this is important for SEO
and accessibility purposes - for exmaple, screen readers will know this
is a navigation menu and as opposed to a standard div tag)

Changed theme stylesheet from a LESS file to a standard CSS file
(located at css/style.css). A minified version is automatically
generated on the next page view whenever changes are made to the source
file. Moved theme styling into this file (this file is loaded after all
the Skeleton theme CSS files so you'll have fewer problems with styles
accidentally being overriden using this one)