Fix duplicate parameters when using ?page_size=

DRF automatically includes ?page_size etc in the next URL, so adding them manually results in duplicate parameters in url.

eg.
/api/feed/?custom_filter=true&custom_filter=true&custom_filter=true&custom_filter=true&custom_filter=true&custom_filter=true&custom_filter=true&custom_filter=true&custom_filter=true&page=10&page_size=5&page_size=5&page_size=5&page_size=5&page_size=5&page_size=5&page_size=5&page_size=5&page_size=5&custom_filter=true&page_size=5
Merge pull request #9 from georgewhewell/master

Fix duplicate parameters when using ?page_size=