Collapse all DummyXX classes into one DummyVirtualSensor

[KyleBenson]

Pretty straightforward. Its constructor could take the type, priority, value, and something specifying how often to send an event. Later the value and how often could be more than just constants (stats distributions?).

[bfrggit]

The real sensors work in different ways. I don't know how we should integrate DummyPIRVS and DummyCSNVS, for example.