OO-450 more meaninfull table header

src/main/java/org/olat/group/ui/main/_i18n/LocalStrings_de.properties

@@ -89,7 +89,7 @@ table.header.leave.waiting=Verlassen
 table.header.login=Benutzername
 table.header.group.full=Voll belegt
 table.header.mark=Favorit
-table.header.online=On
+table.header.online=Chat
 table.header.type=Typ
 table.header.resources=Kurse
 table.header.role=Rolle

src/main/java/org/olat/group/ui/main/_i18n/LocalStrings_en.properties

@@ -143,6 +143,7 @@ table.header.leave.waiting=Leave
 table.header.login=User name
 table.header.mail=E-mail
 table.header.mark=Bookmark
+table.header.online=Chat
 table.header.participants=Participant
 table.header.participantsCount=Assigned
 table.header.remove=Remove