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.
Merge remote-tracking branch 'origin/customerrors' into customerrors