Make tests pass with PYTHONHASHSEED=random

Hello! I believe this is my first patch for a Django-based project, hopefully I'm doing everything right.
I installed the code and ran the tests, but found some failures due to my environment. 

    Due to CVE-2012-1150, CPython now allows using a random seed for hashes,
    so set/dict order is no longer predictable.
    
    Update tests to pass even if the hash seed is randomized.
    Add a testing-only argument to ella.core.templatetags.pagination._do_paginator
    to sort query params before encoding them.

In `test_templatetags.test_params_are_parsed`, I didn't find a good way for to sort a dictionary given to a `for` in a Django template.