[FIX] wrong mail destination address

[FIX] wrong mail destination address when more than 1 attendee is set in the *Attendees* field of meeting.

Without this, ```email_to``` is parsed from
```
'email_to': u' first.attendee@example.com second.attendee@example.com'
```
to
```
'email_to': [u'first.attendee@example.comsecond.attendee', u'@example.com'],
```
and the mail can't be delivered.

With this fix ```email_to``` is parsed to
```
'email_to': [u'first.attendee@example.com', u'second.attendee@example.com']
```
and the mail can be delivered