Change to the 'strong' password policy for relatives

[EmilyTapestrySupport]

To make it less confusing for relatives when they are setting up or resetting their password, we have changed the 'strong' password policy option for them. Now the two requirements are:

• The password must be at least 20 characters
• Must not be a common password, or an obvious variant of the school's name or person's name

This change will not effect any existing passwords or password policies.