css: Make navbar translucent.

Issue #61.
theme: Annotate navbar

Issue #61.
theme: Add inline search

Issue #61.
theme: Use primary color for navbar brand

Issue #61.
css: Remove duplicate attribute

Issue #61.
Add get_header() function

Issue #61.
Use get_header() for D1 mockups

Issue #61.
header.php: Minor refactor
header.php: Add $login_only to get_header()

Issue #61.