Add shared credentials quirk for onsign domains (#1084)

app.onsign.tv and app.onsign.com use the same credential backend.

Author: FranciscoCamerini

quirks/shared-credentials.json

@@ -163,6 +163,12 @@
             "sydneyhealth.com"
         ]
     },
+    {
+        "shared": [
+            "app.onsign.tv",
+            "app.onsign.com"
+        ]
+    },
     {
         "from": [
             "appannie.com"