Make organisation settings platform admin only

At the moment the only setting that a normal organisation team member
can change is the name of the organisation is its name. And we don’t
even want them to be able to change this. So this commit hides the
settings page entirely for non-platform-admin users.

tests/app/main/views/organisations/test_organisation.py

@@ -161,24 +161,16 @@ def test_organisation_trial_mode_services_doesnt_work_if_not_platform_admin(
     )
 
 
-def test_organisation_settings(
+def test_organisation_settings_platform_admin_only(
     client_request,
     mock_get_organisation,
     organisation_one
 ):
-    expected_rows = [
-        'Label Value Action',
-        'Organisation name Org 1 Change',
-    ]
-
-    page = client_request.get('.organisation_settings', org_id=organisation_one['id'])
-
-    assert page.find('h1').text == 'Settings'
-    rows = page.select('tr')
-    assert len(rows) == len(expected_rows)
-    for index, row in enumerate(expected_rows):
-        assert row == " ".join(rows[index].text.split())
-    mock_get_organisation.assert_called_with(organisation_one['id'])
+    client_request.get(
+        '.organisation_settings',
+        org_id=organisation_one['id'],
+        _expected_status=403,
+    )
 
 
 def test_organisation_settings_for_platform_admin(