Clean up Device.__call__()

[mwerezak]

Cleaned up some obvious issues in the code.

• Serialize async callbacks using an actual threading.Lock instead of an error-prone bool. <<< This is probably the most important improvement. The way it was before, if an exception is thrown the device will be stuck permanently "in progress"
• Make kwargs explicit in function signature.
• Remove dead branch, dict.get() will never raise KeyError.
• Replaced commented out try/catch. Close and remove connection if a ConnectionError is raised (while ensuring exception does not get silenced), remove redundant logging call.
• Replace the potentially fragile self-mutating current_selection system with a CommandBuilder class. This makes running a command a more pure computation with all of the mutation happening inside CommandBuilder only. Removed DeviceDuplicate as it no longer serves any useful purpose (you can just duplicate the CommandBuilder object directly).