Add Feed and FeedItem

Also:
* _finalizeErase in Zotero.DataObject is now inheritable
* Call _initErase before starting a DB transaction
* removes Zotero.Libraries.add and Zotero.Libraries.remove (doesn't seem like this is used any more)

test/tests/feedsTest.js

@@ -0,0 +1,59 @@
+describe("Zotero.Feeds", function () {
+	let createFeed = Zotero.Promise.coroutine(function* (props = {}) {
+		let feed = new Zotero.Feed({
+			name: props.name || 'Test ' + Zotero.randomString(),
+			url: props.url || 'http://www.' + Zotero.randomString() + '.com',
+			refreshInterval: props.refreshInterval,
+			cleanupAfter: props.cleanupAfter
+		});
+		
+		yield feed.saveTx();
+		return feed;
+	});
+	
+	let clearFeeds = Zotero.Promise.coroutine(function* () {
+		let feeds = Zotero.Feeds.getAll();
+		yield Zotero.DB.executeTransaction(function* () {
+			for (let i=0; i<feeds.length; i++) {
+				yield feeds[i].erase();
+			}
+		});
+	});
+	
+	describe("#haveFeeds()", function() {
+		it("should return false for a DB without feeds", function* () {
+			yield clearFeeds();
+			assert.isFalse(Zotero.Feeds.haveFeeds(), 'no feeds in empty DB');
+			
+			let group = yield createGroup();
+			
+			assert.isFalse(Zotero.Feeds.haveFeeds(), 'no feeds in DB with groups');
+		});
+		it("should return true for a DB containing feeds", function* () {
+			let feed = yield createFeed();
+			
+			assert.isTrue(Zotero.Feeds.haveFeeds());
+		});
+	});
+	describe("#getAll()", function() {
+		it("should return an empty array for a DB without feeds", function* () {
+			yield clearFeeds();
+			let feeds = Zotero.Feeds.getAll();
+			assert.lengthOf(feeds, 0, 'no feeds in an empty DB');
+			
+			let group = yield createGroup();
+			
+			feeds = Zotero.Feeds.getAll();
+			assert.lengthOf(feeds, 0, 'no feeds in DB with group libraries');
+		});
+		it("should return an array of feeds", function* () {
+			yield clearFeeds();
+			let feed1 = yield createFeed();
+			let feed2 = yield createFeed();
+			
+			let feeds = Zotero.Feeds.getAll();
+			assert.lengthOf(feeds, 2);
+			assert.sameMembers(feeds, [feed1, feed2]);
+		});
+	});
+})