Per-user reblog hiding implementation/fixes/tests

Note that this will only hide/show *future* reblogs by a user, and does
nothing to remove/add reblogs that are already in the timeline. I don't
think that's a particularly confusing behavior, and it's a lot easier
to implement (similar to mutes, I believe).

db/migrate/20171028221157_add_reblogs_to_follows.rb

@@ -0,0 +1,21 @@
+require Rails.root.join('lib', 'mastodon', 'migration_helpers')
+
+class AddReblogsToFollows < ActiveRecord::Migration[5.1]
+  include Mastodon::MigrationHelpers
+
+  safety_assured do
+    disable_ddl_transaction!
+  end
+
+  def up
+    safety_assured do
+      add_column_with_default :follows, :show_reblogs, :boolean, default: true, allow_null: false
+      add_column_with_default :follow_requests, :show_reblogs, :boolean, default: true, allow_null: false
+    end
+  end
+  
+  def down
+    remove_column :follows, :show_reblogs
+    remove_column :follow_requests, :show_reblogs
+  end
+end