Added a new DAO function which archives email reply_to addresses by
setting archived to True. This raises a new type of error, an
ArchiveValidationError, if trying to archive a default reply_to address.
Added a new endpoint for archiving email reply_to addresses.
Updated the DAO methods which return a single email reply_to address and
all reply_to addresses to only return the non-archived addresses.
Changed the type of error that gets raised when using the Admin
interface to be BadRequestError instead of a SQLAlchemyError.
Added a new boolean column, `archived`, with a default of False to the
three models which are used to specify the 'reply to' address for
notifications:
* ServiceEmailReplyTo
* ServiceSmsSender
* ServiceLetterContact