[#707] Implement group_purge action function

This is a rough first implementation, needs tests.
[#707] Add args to group and org purge auth functions

Oops :)
Merge branch 'master' of github.com:okfn/ckan into 707-implement-group-purging
[#707] Add tests for group_purge
[#707] Add tests for organization purging
[#707] Refactor the group_purge tests

Make them more like the organization_purge tests
Merge branch 'master' of github.com:okfn/ckan into 707-implement-group-purging
[#707] Delete accidentally committed .idea/ dir
[#707] Add group_purge and organization_purge docstrings
[#707] PEP8
[#707] Add a docstring to _group_or_org_purge
[#707] Correct a typo in a docstring
[#707] Small _group_or_org_purge refactor
[#707] Remove some unnecessary test code

These actions are not what's being tested here
[#707] Add 'cannot be undone' warnings to *_purge APIs
[#707] Refactor group_ and organization_purge tests

Combine the group and organization purge tests into one test class, to
avoid so much code duplication in the tests.
[#707] Rename group and org purge test module

Now that the one module tests both group and organization purge, it
needs a different name.
[#707] Remove unneeded imports from test_group.py
Merge branch 'master' into 707-implement-group-purging
[#707] Pep8 fixes - trivial