Add requst spec for youtube subscriptions; fix spelling
WIP youtube_subscriptions#update spec
Fix merge conflicts
Fix activities/index.hbs, missing div tag causing styling issues
Add views/click handlers for activity filters
Add view helpers to activities/index.hbs for filtering by provider

Also adds more specific classes for youtube/soundcloud activity in order
to be able to toggle them separately.  jQuery toggle() flips the display
property on the given elements (from block to none) for example.  There
are other ways to do it but it seems to be a good solution, it's super
responsive once all of the activities have been loaded.
Filter checkboxes are 'on' by default

It makes more sense to have them toggled on, ux felt weird with
checkboxes needing to be checked in order to remove a particular
provider from your feed.