Sarah's work to remove slug and owner from new organizations form and refactor view tests

Created by: jogwen

Includes https://github.com/aptivate/econsensus/pull/114

but also covers cards: https://aptivate.kanbantool.com/boards/5986-econsensus#tasks-1549115, https://aptivate.kanbantool.com/boards/5986-econsensus#tasks-1081183, https://aptivate.kanbantool.com/boards/5986-econsensus#tasks-1388793

Also now:

• link to add new org is now an Add link next to title on Your Organizations page (used to be a sentence at bottom of screen
• new test runner means we no longer have to import all tests in tests/init.py
• new Decision only gets is_active org members as watchers, not just all org members.