fixed bug and added support for multiple schedules in schedule silencing

When `silence_for` is specified we should only silence/clear one group,
I introduced a bug a few commits ago that would ignore the group and
silence/clear based on date. Use the silence_for window to match and
clear the first group.

Also added support for comma separate string on `silence_type` option.
In the MCH case we have two schedules that can be generated depending on
the form submission/registration: ANC Reminders and ANC Reminders LMP.
Now both schedules can be cleared with a single ANCV settings entry.