Mobile filtering nav for developer materials

Developer materials mobile filtering + layout. Resolves DEVELOPER-367

Demos table - responsive and desktop

Should fix (or at least mostly) DEVELOPER-270

We may need to refine the projects used in each product, but the
ground work is done.

We're reusing what was done in the projects page to maintain
consistency.

Removed commented out code

Fixing events page sprites and spacing, resolves DEVELOPER-362

Fixing mobile layout errors that sprites introduced, resolves DEVELOPER-363