Add pagination for all other routes

[Trayshar]

I added serverside keyset pagination for the /calls route in #2 using Paginator. The following routes have not yet been changed:

• /transmitters
• /users
• /rubrics
• /subscribers
• /nodes

The approach used in /calls won't work for routes using CouchDB as database. Luckily, CouchDB does have documentation on that matter

A way to apply a filter is also necessary, perhaps through an additional WHERE clause.