DRY up reblog vs original status check

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.

app/helpers/stream_entries_helper.rb

@@ -34,10 +34,6 @@ module StreamEntriesHelper
     user_signed_in? && @favourited.key?(status.id) ? 'favourited' : ''
   end
 
-  def proper_status(status)
-    status.reblog? ? status.reblog : status
-  end
-
   def rtl?(text)
     return false if text.empty?