full service crashes with DB is disconnected

[mejohnnaylor]

libc++abi: terminating due to uncaught exception of type catena::exception_with_status: setValue failed: mutex lock failed: Invalid argument void catena::ParamAccessor::setValue(const V &) [Threadsafe = true, V = int]

steps to reproduce:

• run full_service (I had it with secure comms going but don't think this is needed to trigger this behavior)
• connect up DB
• remove the connection from DB, this will cause full_service to crash

[mejohnnaylor]

I found what looks to be the problem. https://github.com/vdksoft/signals/blob/master/demo/basic_demo.cpp is the signals library we're using. The Connect objects form a connection to the DeviceModel object on creation, but DO NOT disconnect on destruction. So the DM continues to send updates to the Connect object after it's deleted. Fix is to add the disconnect call at appropriate junctures. Assigning to John