Billboard is now inline, and does not have a fixed position

- Fixes issue where fork me link could appear out of position
- Fixes issue where project copy could overflow billboard (e.g. if long, or altering zoom/text-size)

[Finishes #55911300]
Merge commit '3997006cc1246a52ed38ebed77e0f5827ac2a4bd' into gh-pages

# By Phillip Webb
# Via Phillip Webb
* commit '3997006cc1246a52ed38ebed77e0f5827ac2a4bd':
  Protect against no 'current' project version
  Extract base_layout to page include
  Update highlightlng for maven and gradle snippets

Conflicts:
	_layouts/base_layout.html