Add Context of type "double" to probed values

There are strong reason to only allow context of type "int" and "string" in the ProbeBus. Else a comparison using "==" does not make too much sense. Anyways this limitation leads to strange workarounds at many points, since context is not only used for sorting. For example the channel casts x-y-z position info to "int" just to pass it as context.
I suggest allowing "double" context, maybe find a way to prevent it to be used in "==" sorting. And if possible even allow more complex sorting expressions using "<" and ">" etc.