[SSK] serialize all read/write to sessionStore

Attempt to avoid session corruption happening due to an inconsistent
view of the session store by ensuring all access to the session store
happens on a serialized queue

// FREEBIE

Podfile

@@ -5,7 +5,7 @@ target 'Signal' do
     pod 'SocketRocket',               :git => 'https://github.com/facebook/SocketRocket.git'
     pod 'AxolotlKit',                 git: 'https://github.com/WhisperSystems/SignalProtocolKit.git'
     #pod 'AxolotlKit',                 path: '../SignalProtocolKit'
-    pod 'SignalServiceKit',           git: 'https://github.com/WhisperSystems/SignalServiceKit.git', commit: '7578176e378c4602b5295f97c3329d254498523b'
+    pod 'SignalServiceKit',           git: 'https://github.com/WhisperSystems/SignalServiceKit.git'
     #pod 'SignalServiceKit',           path: '../SignalServiceKit'
     pod 'OpenSSL'
     pod 'SCWaveformView',             '~> 1.0'

Podfile.lock

@@ -116,14 +116,13 @@ DEPENDENCIES:
   - OpenSSL
   - PureLayout
   - SCWaveformView (~> 1.0)
-  - SignalServiceKit (from `https://github.com/WhisperSystems/SignalServiceKit.git`, commit `7578176e378c4602b5295f97c3329d254498523b`)
+  - SignalServiceKit (from `https://github.com/WhisperSystems/SignalServiceKit.git`)
   - SocketRocket (from `https://github.com/facebook/SocketRocket.git`)
 
 EXTERNAL SOURCES:
   AxolotlKit:
     :git: https://github.com/WhisperSystems/SignalProtocolKit.git
   SignalServiceKit:
-    :commit: 7578176e378c4602b5295f97c3329d254498523b
     :git: https://github.com/WhisperSystems/SignalServiceKit.git
   SocketRocket:
     :git: https://github.com/facebook/SocketRocket.git
@@ -133,7 +132,7 @@ CHECKOUT OPTIONS:
     :commit: cbf2f47d59dd54d6d720fe787f835bd767443bb6
     :git: https://github.com/WhisperSystems/SignalProtocolKit.git
   SignalServiceKit:
-    :commit: 7578176e378c4602b5295f97c3329d254498523b
+    :commit: 45b8dc9c96fe3aeb6e0c46eff7912670d2fc41a9
     :git: https://github.com/WhisperSystems/SignalServiceKit.git
   SocketRocket:
     :commit: 877ac7438be3ad0b45ef5ca3969574e4b97112bf
@@ -162,6 +161,6 @@ SPEC CHECKSUMS:
   UnionFind: c33be5adb12983981d6e827ea94fc7f9e370f52d
   YapDatabase: b1e43555a34a5298e23a045be96817a5ef0da58f
 
-PODFILE CHECKSUM: 29bf376adcb82f35d46545ccdb7c77522af4f155
+PODFILE CHECKSUM: a060377074cb361576f346a58d1503b3bd708440
 
 COCOAPODS: 1.2.0