[api] support event mails to group mail adresses

Sends mail to defined group email address if defined, otherwise to group members
as before.

There is no way atm to defined a group email adress, but to suppress mails to it.
[api] make debug output useful in test suite

not just showing backtrace to HoptoaddNotifier
[api] support event mails to group mail adresses

Sends mail to defined group email address if defined, otherwise to group members
as before.

There is no way atm to defined a group email adress, but to suppress mails to it.