Move ASTableView & ASCollectionView data fetching to background thread

Conflicts:
	AsyncDisplayKit/ASCollectionView.mm
	AsyncDisplayKit/Details/ASDataController.mm

Conflicts:
	AsyncDisplayKit/ASCollectionView.mm
	AsyncDisplayKit/Details/ASDataController.mm

AsyncDisplayKit/ASTableView.mm

@@ -112,6 +112,8 @@ static BOOL _isInterceptedSelector(SEL sel)
   ASRangeController *_rangeController;
 }
 
+@property (atomic, assign) BOOL asyncDataSouceLocked;
+
 @end
 
 @implementation ASTableView
@@ -137,6 +139,8 @@ static BOOL _isInterceptedSelector(SEL sel)
   _proxyDelegate = [[_ASTableViewProxy alloc] initWithTarget:nil interceptor:self];
   super.delegate = (id<UITableViewDelegate>)_proxyDelegate;
 
+  _asyncDataSouceLocked = NO;
+
   return self;
 }
 
@@ -425,6 +429,28 @@ static BOOL _isInterceptedSelector(SEL sel)
   return CGSizeMake(self.bounds.size.width, FLT_MAX);
 }
 
+- (void)dataControllerLockDataSourceForDataUpdating
+{
+  ASDisplayNodeAssert(!self.asyncDataSouceLocked, @"The data source has already been locked !");
+
+  self.asyncDataSouceLocked = YES;
+
+  if ([_asyncDataSource respondsToSelector:@selector(tableViewLockDataSourceForDataUpdating:)]) {
+    [_asyncDataSource tableViewLockDataSourceForDataUpdating:self];
+  }
+}
+
+- (void)dataControllerUnlockDataSourceForDataUpdating
+{
+  ASDisplayNodeAssert(self.asyncDataSouceLocked, @"The data source has already been unlocked !");
+
+  self.asyncDataSouceLocked = NO;
+
+  if ([_asyncDataSource respondsToSelector:@selector(tableViewUnlockDataSourceForDataUpdating:)]) {
+    [_asyncDataSource tableViewUnlockDataSourceForDataUpdating:self];
+  }
+}
+
 - (NSUInteger)dataController:(ASDataController *)dataControllre rowsInSection:(NSUInteger)section
 {
   return [_asyncDataSource tableView:self numberOfRowsInSection:section];