Add paging to folder contents REST API

[dave-kennedy]

Given a folder can have hundreds of children, it would be good to have paging on the new folder contents endpoint in the REST API. Something like:

get:: /public/rest/v2/folder/(int:folder_id)/children

:query int page: if this is non-negative, results will be paginated by 10 children per page. Default: ``0``.

I understand you've got a few issues on your hands. No rush :)

[salavursa]

@marcelklehr any thoughts here if this can be discussed/implemented?