Allow a Role to be toggled automatically based on subscription status

[benjie]

Don't get Role until paidUntil > today; automatically drop Role when paidUntil is at least n months in the past (where n >= 1).

Both the role and n should be configurable.

Trigger logic a few minutes after startup and then daily?

[benjie]

Using the latest role rejection code, the user will automatically be notified via email, thereby prodding them to update their payment details. Add a configuration variable for rejectionMessage