New Strava and Google Analytics Services, fixed Fitbit token refreshing

• Enhancement: Added a Google Analytics Service definition, props @superbia.
• Enhancement: Added a Strava Service definition, props @mdrovdahl.
• Enhancement: Add a "Settings" link to the plugin listing if you're using the bundled Admin UI.
• Bugfix: Remove deprecated calls to screen_icon().
• Bugfix: Fitbit tokens now refresh automatically.
• Bugfix: Tumblr now requires HTTPS, so update all request URLs. Props @westi.