Add tests for paged/filtered groups & update fixtures

memopol/tests/base.py

...nse_fixtures/GroupListTest.test_active_committees/content

...se_fixtures/GroupListTest.test_active_delegations/content

...sponse_fixtures/GroupListTest.test_active_parties/content

...sponse_fixtures/GroupListTest.test_all_committees/content

...ponse_fixtures/GroupListTest.test_all_delegations/content

.../response_fixtures/GroupListTest.test_all_parties/content

...sts/response_fixtures/GroupListTest.test_chambers/content

...s/response_fixtures/GroupListTest.test_committees/content

...ests/response_fixtures/GroupListTest.test_country/content

.../response_fixtures/GroupListTest.test_delegations/content

...ests/response_fixtures/GroupListTest.test_parties/content

memopol/tests/test_dossiers.py

memopol/tests/test_group_list.py