User Setting Registration Defaults

User Setting Registration Defaults

Add a new reg_default value for user setting types. On patron registration
the value (if any) is used as a default for the patron.

Only applicable to those settings editable via the patron editor.

Intended use cases:

1 - Hold Notification Type Default other than phone:email
2 - A/T user settings defaulting to "on" at registration

Signed-off-by: Thomas Berezansky <tsbere@mvlc.org>