Update gem show styles

Update dockyard footer outbound link
Firefox search box alignment
Better icons
Remove clippy
Add zeroclipboard
Merge pull request #761 from rubygems/736-ac-gem-detail-update

Update gem show styles
fix latest_version_number helper
update status page links to HTTPS
#750 - New header nav hover styles
Merge pull request #763 from rubygems/750-ac-nav-contrast

Closes #750 - New header nav hover styles
Enable asset pipeline and Autoprefixer
Cleanup stylesheets
Enable assets