Implement the two pending specs on `Status`: `reblogs_count` and
`favourites_count`.

Checking reblog vs original status was happening in multiple places
across the app. For views, this logic was encapsulated in a helper
method named `proper_status` but in the other layers of the app, the
logic was duplicated.

Because the logic is used at all layers of the app, we extracted it into
a `Status#proper` method on the model and changed all uses of the logic
to use this method. There is now a single source of truth for this
condition.

We added test coverage to untested methods that got refactored.

This adds the ability to filter user signup with a whitelist
instead of or in addition to a blacklist.

Fixes #817

Fix anchor tags in some wikipedia URLs being matches as a hashtag

StreamEntry model. Simply render Salmon slaps as they are needed

Try to fix Travis CI setup

Reflect "requested" relationship in API and UI
Reflect inability of private posts to be reblogged in the UI
Disable Webfinger for locked accounts

as well as formatting of content

and atom feed generation to some extent, as well as the way mentions are
stored

relations on Status#mentions