Adds VS App Center analytics + crash reporting

Currently tracks install, refresh, and update app events.

Pods/AppCenter/AppCenter-SDK-Apple/iOS/AppCenter.framework/Headers/MSServiceAbstract.h

@@ -0,0 +1,55 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+#ifndef MS_SERVICE_ABSTRACT_H
+#define MS_SERVICE_ABSTRACT_H
+
+#import <Foundation/Foundation.h>
+
+#import "MSService.h"
+
+@protocol MSChannelGroupProtocol;
+
+/**
+ * Abstraction of services common logic.
+ * This class is intended to be subclassed only not instantiated directly.
+ */
+@interface MSServiceAbstract : NSObject <MSService>
+
+/**
+ * The flag indicates whether the service is started from application or not.
+ */
+@property(nonatomic, assign) BOOL startedFromApplication;
+
+/**
+ * Start this service with a channel group. Also sets the flag that indicates that a service has been started.
+ *
+ * @param channelGroup channel group used to persist and send logs.
+ * @param appSecret app secret for the SDK.
+ * @param token default transmission target token for this service.
+ * @param fromApplication indicates whether the service started from an application or not.
+ */
+- (void)startWithChannelGroup:(id<MSChannelGroupProtocol>)channelGroup
+                    appSecret:(NSString *)appSecret
+      transmissionTargetToken:(NSString *)token
+              fromApplication:(BOOL)fromApplication;
+
+/**
+ * Update configuration when the service requires to start again. This method should only be called if the service is started from libraries
+ * and then is being started from an application.
+ *
+ * @param appSecret app secret for the SDK.
+ * @param token default transmission target token for this service.
+ */
+- (void)updateConfigurationWithAppSecret:(NSString *)appSecret transmissionTargetToken:(NSString *)token;
+
+/**
+ * Checks if the service needs the application secret.
+ *
+ * @return `YES` if the application secret is required, `NO` otherwise.
+ */
+- (BOOL)isAppSecretRequired;
+
+@end
+
+#endif