Refractor and optimize AP collections

Only display urls in general object, and paginate video comments, shares, likes and
dislikes

server/controllers/activitypub/utils.ts

@@ -0,0 +1,11 @@
+import * as express from 'express'
+
+function activityPubResponse (data: any, res: express.Response) {
+  return res.type('application/activity+json; charset=utf-8')
+            .json(data)
+            .end()
+}
+
+export {
+  activityPubResponse
+}