Rename icon_for_service() to omniauth_provider_icon().
Add omniauth_provider_name().
Use yes_no().
Add omniauth_button() and use some Sass tricks for DRY.
Alter the caption text format for services.

"(Twitter) knu" -> "Twitter: knu"
Show the service in Agent details page, styled as a label.
Set the button color for Tumblr.
Merge branch 'services_views'