AppleScript: Add a "feed" property to articles

- Also make scripts like

feed id "foo" of account id "bar"

find feeds in folders.

Mac/Resources/NetNewsWire.sdef

@@ -216,7 +216,10 @@
             <property name="image url" code="IURL" type="text" access="r" description="an image url for the article">
                 <cocoa key="imageURL"/>
             </property>
-            <element type="author">
+            <property name="feed" code="Feed" type="webFeed" access="r" description="the containing feed">
+                <cocoa key="feed"/>
+            </property>
+			<element type="author">
                 <cocoa key="authors"/>
             </element>
         </class>

Mac/Scriptability/Account+Scriptability.swift

@@ -101,14 +101,13 @@ class ScriptableAccount: NSObject, UniqueIdScriptingObject, ScriptingObjectConta
     
     @objc(valueInWebFeedsWithUniqueID:)
     func valueInWebFeeds(withUniqueID id:String) -> ScriptableWebFeed? {
-        let feeds = Array(account.topLevelWebFeeds)
-        guard let feed = feeds.first(where:{$0.webFeedID == id}) else { return nil }
+		guard let feed = account.existingWebFeed(withWebFeedID: id) else { return nil }
         return ScriptableWebFeed(feed, container:self)
     }
     
     @objc(valueInWebFeedsWithName:)
     func valueInWebFeeds(withName name:String) -> ScriptableWebFeed? {
-		let feeds = Array(account.topLevelWebFeeds)
+		let feeds = Array(account.flattenedWebFeeds())
         guard let feed = feeds.first(where:{$0.name == name}) else { return nil }
         return ScriptableWebFeed(feed, container:self)
     }

Mac/Scriptability/Article+Scriptability.swift

@@ -141,4 +141,13 @@ class ScriptableArticle: NSObject, UniqueIdScriptingObject, ScriptingObjectConta
         return articleAuthors.map { ScriptableAuthor($0, container:self) } as NSArray
     }
 
+	@objc(feed)
+	var feed: ScriptableWebFeed? {
+		guard let parentFeed = self.article.webFeed,
+			let account = parentFeed.account
+			else { return nil }
+
+		return ScriptableWebFeed(parentFeed, container: ScriptableAccount(account))
+	}
+
 }