More compliance with the OLA RDM Tests

Compliance with the OLA RDM Tests around sub devices and mute messages. Also with @nightrune get device specific PIDs returning properly in supportedParameters. Also make the device specific PIDs compliant with the OLA RDM Tests. Add device model ID option.

I has also found a bug, which exists with the January code before I touched it, running the following sequence of sets and gets causes timouts or similar messages during the RDM comms:

ola_rdm_set -u 2 --uid 0987:201269c6 device_label "test_label"; ola_rdm_get -u 2 --uid 0987:201269c6 device_label; ola_rdm_set -u 2 --uid 0987:201269c6 device_label "test_labe"; ola_rdm_set -u 2 --uid 0987:201269c6 device_label 'a'