Revert to using fieldmangler for adding fields

In 5.1.5 we switched to using `<$action-setfield>` instead of
`<$fieldmangler>`. The problem was that in the process we lost the
validation of field names, making it possible to create fields with
illegal names

Fixes #1186

core/modules/widgets/fieldmangler.js

@@ -71,24 +71,38 @@ FieldManglerWidget.prototype.handleRemoveFieldEvent = function(event) {
 };
 
 FieldManglerWidget.prototype.handleAddFieldEvent = function(event) {
-	var tiddler = this.wiki.getTiddler(this.mangleTitle);
-	if(tiddler && typeof event.param === "string") {
-		var name = event.param.toLowerCase().trim();
-		if(name !== "" && !$tw.utils.hop(tiddler.fields,name)) {
-			if(!$tw.utils.isValidFieldName(name)) {
-				alert($tw.language.getString(
-					"InvalidFieldName",
-					{variables:
-						{fieldName: name}
-					}
-				));
-				return true;
+	var tiddler = this.wiki.getTiddler(this.mangleTitle),
+		addition = this.wiki.getModificationFields(),
+		hadInvalidFieldName = false,
+		addField = function(name,value) {
+			var trimmedName = name.toLowerCase().trim();
+	debugger;
+			if(!$tw.utils.isValidFieldName(trimmedName)) {
+				if(!hadInvalidFieldName) {
+					alert($tw.language.getString(
+						"InvalidFieldName",
+						{variables:
+							{fieldName: trimmedName}
+						}
+					));
+					hadInvalidFieldName = true;
+					return;
+				}
+			} else {
+				addition[trimmedName] = value || "";
 			}
-			var addition = this.wiki.getModificationFields();
-			addition[name] = "";
-			this.wiki.addTiddler(new $tw.Tiddler(tiddler,addition));
+			return;
+		};
+	addition.title = this.mangleTitle;
+	if(typeof event.param === "string") {
+		addField(event.param,"");
+	}
+	if(typeof event.paramObject === "object") {
+		for(var name in event.paramObject) {
+			addField(name,event.paramObject[name]);
 		}
 	}
+	this.wiki.addTiddler(new $tw.Tiddler(tiddler,addition));
 	return true;
 };