Catch and send exceptions that occur in SendingMessage event handlers.
Renamed private field
Moved new SendingMessage logic to base class to be shared by more providers.
Added improved SendingMessage logic to WP, iOS and Android
Added improved SendingMessage logic to Mac provider
Added improved SendingMessage logic to WinRT and WindowsStore
Unit tests
Merge pull request #195 from MindscapeHQ/Catch-sending-message-handler-crashes

Catch sending message handler crashes