If we say that the version format should be the same for the `version_lowest`
and the `version_bootloader` then it does not always make sense to set it at
the same time.
Moving the `version_format` to a standalone first-class property also means it
can be typically be set in the custom device `_init()` function, which means we
don't need to worry about *changing* ther version format as set by the USB and
UDev superclass helpers.
In some hardware there are two identical USB hubs with different firmware.
One is upstream, and one is downstream, making up to 7 user-available ports.
Use the 'removable' bitfield to target the proper firmware to the correct
device, on the logic that the setting will be different on upstream (removable)
and downstream (non-removable, as on the same PCB) hubs.
