ErrorController and associated views added.

Added actions to ErrorController for handling 500, 404, and 401 HTTP status codes.

Added the respective views, with a stripped down layout file for HTTP error pages.
Glimpse logo added to error page headers.

Views and associated LESS files updated, regular site footer added to
_ErrorLayout.cshtml, and ContactInfo.cshtml partial view removed.
Configured <httpErrors> in web.config.

Added custom error pages for 401, 404, and 500 HTTP status codes that
use the corresponding views from the ErrorController.
Removed global.min.css from csproj file.

I'd mistakenly added a global.min.css file to the Glimpse.Site.csproj
file. This has now been removed.

Also, I've changed the CSS formatting in global.css to use Visual
Studio's compact rules.
Navigation bar added to error pages.

Added the navigation bar to the error pages, and moved the heading into the page.
Merge pull request #29 from ianoxley/customerrors

Custom error pages added