hameg-hmo: Add RTB2000 and RTM3000 MSO support (untested).
According to the latest available version of the manual, they
both use a slightly different dialect than currently supported
models, in particular when it comes to the POD (logic channel
groups) handling.
I do not have any of the above models available for testing
therefore I do not know whether or not they also understand
the existing dialect. In doubt, the new official dialect is
implemented by this patch.