Add date-based paging support to EndpointPaging

[rinukkusu]

In PR #66 date-based paging has been added to the me.recentlyPlayed() endpoint.
As a developer I'd like to use this kind of paging in other places as well, so it would be great to have it implemented in EndpointPaging itself directly. We'll probably need seperate paging classes for offset- and date-based paging.

[hayribakici]

It would be good to know, which API endpoints are providing the before or after query parameters. So far, I have seen it only in the recently-played endpoint. Do you know any other?

[rinukkusu]

True, I have not yet investigated which endpoints are actually using that. If we find out, that recently-played is the only one - great, then we can close the PR 😄

[thosakwe]

Were there any other endpoints that use date-based paging?

[hayribakici]

I looked it into today and so far only the recenty-played endpoint has a timestamp (before and after) query parameters.
If you would like, you can also check it out here.