AccountsDialog: Truncate too long account names
AccountsDialog: Truncate too long account names

This prevent strings to be too big.

https://bugzilla.gnome.org/show_bug.cgi?id=702095

Distrotech/telepathy-account-widgets,GNOME/telepathy-account-widgets,Distrotech/telepathy-account-widgets,GNOME/telepathy-account-widgets,GNOME/telepathy-account-widgets