Enable notify checking for holds in A/T Validators

Enable notify checking for holds in A/T Validators

HoldIsAvailable and HoldIsCanceled get new checks, plus add HoldNotifyCheck
validator.

All three check for "check_$type_notify" parameters evaling to true, where
$type is email, sms, or phone. If true the hold's appropriate value is
checked and, if not suitable, the validator returns false.

For email the email_notify value must pass the is_true test.

For sms/phone the appropriate notify value must pass perl's truth test.

Upgrade script modifies default event definitions, with the exception of
the sms hold available event definition. That has no static id in the seed
values.

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