Allow a way to "abort" an email

[sbrossie]

In some situation we would like to to sending emails to specific users -- users explicitly asked to not receive emails, or account is in bad state and we don't want to email anything until fixed.

• For accounts in bad state __PARKED__, we should in any case disable sending any email
• We currently have a isNotifiedForinvoice attribute at the account level. Maybe we could rename it to be more generic ON/OFF switch that disable at the account level any form of email sending?