Nodes referencing a device can be bound later than the device is
bound. If this happens, the node will not receive an initial route
device volume change event. This change caches the last known route
device volume and initializes the device with it if present.
Previously a hardcoded 0.0001 offset was used to determine if a volume
change was significant enough to send to a device, however some
devices have a much more granular step size, which caused future
volume updates to be blocked.
This change replaces the hardcoded offset with the volumeStep device
route property which should be large enough for the device to work with.
Fixes#279