Add :focus styling for links

Better keyboard accessibility.

https://twitter.com/patrick_h_lauke/status/353058140142571521
Update Firefox OS page title bug 888861
Merge pull request #1020 from alexgibson/update-page-title-firefox-os-bug-888861

Update Firefox OS page title bug 888861
Merge pull request #1036 from craigcook/master

Add :focus styling for links
return 500 in lib.bedrock_util.server_error_view