Overhaul our logging, add activity tracing support. (#399)

* Improve the os_log and os_activity integration

* Address feedback from Scott and Huy

examples/CatDealsCollectionView/Sample/ItemViewModel.h

@@ -1,20 +1,18 @@
 //
 //  ItemViewModel.h
-//  Sample
-//
-//  Created by Samuel Stow on 12/29/15.
+//  Texture
 //
 //  Copyright (c) 2014-present, Facebook, Inc.  All rights reserved.
 //  This source code is licensed under the BSD-style license found in the
-//  LICENSE file in the root directory of this source tree. An additional grant
-//  of patent rights can be found in the PATENTS file in the same directory.
+//  LICENSE file in the /ASDK-Licenses directory of this source tree. An additional
+//  grant of patent rights can be found in the PATENTS file in the same directory.
 //
-//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
-//  FACEBOOK BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
-//  ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
-//  CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+//  Modifications to this file made after 4/13/2017 are: Copyright (c) 2017-present,
+//  Pinterest, Inc.  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 <Foundation/Foundation.h>
@@ -22,8 +20,9 @@
 
 @interface ItemViewModel : NSObject
 
-+ (instancetype)randomItem;
++ (ItemViewModel *)randomItem;
 
+@property (nonatomic, readonly) NSInteger identifier;
 @property (nonatomic, copy) NSString *titleText;
 @property (nonatomic, copy) NSString *firstInfoText;
 @property (nonatomic, copy) NSString *secondInfoText;