Fix TemplateParser::getFirstNameFromEmail

The function now correctly returns the first name if the mail address has the form

* 'FirstName LastName' <foo@mail.xx>
* 'LastName, FirstName' <foo@mail.xx>
* foo@mail.xx

In the first two cases 'FirstName' should be returned, in the third case
the part before the '@' (i.e. 'foo' in this example).