DontDieInTheStore - handling exceptions in receive in websocket store transport

If an exception happened while reading a message using the websocket store transport we would not handle. As a result it would be bubbled up and would crash the user's app. The user have no way of catching this exception. The fix is to catch exceptions and report them to the user using the IConnection.Error and to close the websocket to enable reconnect logic.

Workitem #3313
Removed await from RedisMessageBus.Send

- The await would cause an unnecessary SyncContext.Post that would prevent
  the returned Task from completing if there was a thread blocked on the
  returned Task while holding the SyncConetext.

#3240
Update Client.Store platform moniker to portable-win81+wpa81

- Previously, when I tried installing the client package into a universal app,
  only the phone project got the additional dll with WebSocket support.