Addendum to #253
Addendum to #253

The sg plugin didn't receive tokenAdded/Removed handling yet. This
commit fixes it.

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