[example/CustomCollectionView] Implement MosaicCollectionLayoutDelegate (#28)

* Implement MosaicCollectionLayoutDelegate

* Update licenses

* Address comments

* Fix license

examples/CustomCollectionView/Sample/MosaicCollectionLayoutDelegate.h

@@ -0,0 +1,20 @@
+//
+//  MosaicCollectionLayoutDelegate.h
+//  Texture
+//
+//  Copyright (c) 2017-present, Pinterest, Inc.  All rights reserved.
+//  Licensed under the Apache License, Version 2.0 (the "License");
+//  you may not use this file except in compliance with the License.
+//  You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+
+#import <UIKit/UIKit.h>
+#import <AsyncDisplayKit/AsyncDisplayKit.h>
+
+@interface MosaicCollectionLayoutDelegate : NSObject <ASCollectionLayoutDelegate>
+
+- (instancetype)initWithNumberOfColumns:(NSInteger)numberOfColumns headerHeight:(CGFloat)headerHeight;
+
+@end