Add UI flow to generate flyers

Logic/UIEventSource.ts

@@ -678,6 +678,18 @@ export class UIEventSource<T> extends Store<T> {
     public map<J>(f: (t: T) => J, extraSources: Store<any>[] = []): Store<J> {
         return new MappedStore(this, f, extraSources, this._callbacks, f(this.data))
     }
+    /**
+     * Monoidal map which results in a read-only store. 'undefined' is passed 'as is'
+     * Given a function 'f', will construct a new UIEventSource where the contents will always be "f(this.data)'
+        */
+    public mapD<J>(f: (t: T) => J, extraSources: Store<any>[] = []): Store<J | undefined> {
+        return new MappedStore(this, t => {
+            if(t === undefined){
+                return undefined
+            }
+            return f(t)
+        }, extraSources, this._callbacks, this.data === undefined ? undefined : f(this.data))
+    }
 
     /**
      * Two way sync with functions in both directions

Logic/Web/QueryParameters.ts

@@ -108,4 +108,11 @@ export class QueryParameters {
             history.replaceState(null, "", "?" + parts.join("&") + Hash.Current())
         }
     }
+
+    static ClearAll() {
+        for (const name in QueryParameters.knownSources) {
+            QueryParameters.knownSources[name].setData("")
+        }
+        QueryParameters._wasInitialized.clear()
+    }
 }