Member API shows duplicates and skippes some members

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Found it on production system: https://lataamo.helsinki.hacklab.fi/api/members/?format=json

To reproduce:

1. Follow next link of JSON document recursively and collect the results
2. Total count of elements in results object matches the real member count
3. However, the same members may show up on different pages and some members are not visible at all

This might be pagination or sorting issue. This prevents all API usage, because it's not reliable enough.