Ensure that deleting sessions happens on session queue

// FREEBIE

src/Messages/InvalidKeyMessages/TSInvalidIdentityKeyReceivingErrorMessage.m

@@ -1,5 +1,6 @@
-//  Created by Frederic Jacobs on 31/12/14.
+//
-//  Copyright (c) 2014 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
 
 #import "TSInvalidIdentityKeyReceivingErrorMessage.h"
 #import "OWSFingerprint.h"
@@ -78,8 +79,11 @@ NS_ASSUME_NONNULL_BEGIN
         return;
     }
 
+    // Saving a new identity mutates the session store so it must happen on the sessionStoreQueue
+    dispatch_async([OWSDispatch sessionStoreQueue], ^{
         [[TSStorageManager sharedManager] saveRemoteIdentity:newKey recipientId:self.envelope.source];
 
+        dispatch_async(dispatch_get_main_queue(), ^{
             // Decrypt this and any old messages for the newly accepted key
             NSArray<TSInvalidIdentityKeyReceivingErrorMessage *> *messagesToDecrypt =
                 [self.thread receivedMessagesForInvalidKey:newKey];
@@ -92,6 +96,8 @@ NS_ASSUME_NONNULL_BEGIN
                 //  2.) fail and create a new identical error message in the thread.
                 [errorMessage remove];
             }
+        });
+    });
 }
 
 - (NSData *)newIdentityKey

src/Messages/InvalidKeyMessages/TSInvalidIdentityKeySendingErrorMessage.m

@@ -1,5 +1,6 @@
-//  Created by Frederic Jacobs on 15/02/15.
+//
-//  Copyright (c) 2015 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
 
 #import "TSInvalidIdentityKeySendingErrorMessage.h"
 #import "OWSFingerprint.h"
@@ -56,7 +57,10 @@ NSString *TSInvalidRecipientKey = @"TSInvalidRecipientKey";
 
 - (void)acceptNewIdentityKey
 {
+    // Saving a new identity mutates the session store so it must happen on the sessionStoreQueue
+    dispatch_async([OWSDispatch sessionStoreQueue], ^{
         [[TSStorageManager sharedManager] saveRemoteIdentity:self.newIdentityKey recipientId:self.recipientId];
+    });
 }
 
 - (NSData *)newIdentityKey

src/Messages/TSMessagesManager.m

@@ -581,7 +581,9 @@ NS_ASSUME_NONNULL_BEGIN
         }
     }];
 
+    dispatch_async([OWSDispatch sessionStoreQueue], ^{
         [[TSStorageManager sharedManager] deleteAllSessionsForContact:endSessionEnvelope.source];
+    });
 }
 
 - (void)handleExpirationTimerUpdateMessageWithEnvelope:(OWSSignalServiceProtosEnvelope *)envelope