Add forum setting to permanently anonymize

[chadbrower0]

This change adds another forum setting toggle to make anonymization permanent. There are constraints between the anonymize and permanent toggles:

• Anonymize must be on before permanent can be on
• Once permanent is on, neither toggle can change

An alternative user interface could be drop-down menu holding the three possible anonymization states: {off, temporary, permanent}. But adding a new toggle was chosen for consistency with the current UI and data model.

[tkriplean]

This is awesome! We're close to merging.