Parameter comparison dialog

[vasarhelyi]

It would be great to have a new dialog where one could define one (or more) parameters that should be retrieved from all drones for comparison. First obvious use case is the firmware version ("are all my drones updated to the proper firmware?"), but any other check on autopilot settings can be useful. The dialog should summarize the results as a set with IDs belonging to each value of the retrieved parameters to be able to visualize any difference from the possible common value (such as in the GPS status widget). Code can be reused from parameter upload dialog as this is probably mostly a subset of that tool.

[vasarhelyi]

Actually, a short additional note is that the "version" command in Skybrush is not an autopilot parameter, so these two things should be distinguished: 1) send commands to all drones and wait for response to compare 2) request a parameter value from the autopilot and compare