Forcing page counts onto upstream URLs broke v2 proxying partially

[briantist]

In #104 I had all upstream requests add on query string parameters to set the page size to 100, which helps reduce number of roundtrips with old clients, and slightly mitigates #99.

The page size parameters are different between v2 and v3, page_size and limit respectively and I lazily just added both to all URLs.

But it turns out that old galaxy throws a 400 error on the parameter it doesn't recognize, so that's causing failures on some paginated requests.