Make notifier configurable
Make notifier configurable

And make use of default values in case such a configuration wasn't
specified.

Masoumeh/arethusa,alpheios-project/arethusa,alpheios-project/arethusa,alpheios-project/arethusa,Masoumeh/arethusa,latin-language-toolkit/arethusa,PonteIneptique/arethusa,fbaumgardt/arethusa,fbaumgardt/arethusa,PonteIneptique/arethusa,latin-language-toolkit/arethusa,fbaumgardt/arethusa