Add SyncActivity service for Quickbooks Windows

I added the SyncActivity call to the Quickbooks API. This call is unique in the way it was built (I'm pretty sure). It doesn't really fit with the way the other calls were written. I took a bit of a custom approach and added the code to the service directly.

Let me know if you'd like me to change the way this is built or add an explanation of how to use this to the README.

Thanks! :grinning: