@chrisndodge added paging meta information in unit tests.
@martynjames Yeah JSON response would be `null` instead of `None`
I have added the ability to set `page_size` by client via QueryString `/api/users?page_size=15`
It'll first parse QueryString to get `page_size` if it fails it'll get it from `API_PAGE_SIZE` LMS setting and if still fails it'll get default value of 20