add flag to ruleset that indicates a message is forwarded, slightly modifying how junk analysis is done

part of PR #50 by bobobo1618

webaccount/accountapi.json

@@ -169,6 +169,13 @@
 						"string"
 					]
 				},
+				{
+					"Name": "IsForward",
+					"Docs": "todo: once we implement ARC, we can use dkim domains that we cannot verify but that the arc-verified forwarding mail server was able to verify.",
+					"Typewords": [
+						"bool"
+					]
+				},
 				{
 					"Name": "ListAllowDomain",
 					"Docs": "",