More stringent differentiating between enc1.0 and enc2.0 panel parts (bottom panel)

[Alphaprot]

Moving to Enclosure 2.0 as the now default option for V-Core 3.1 enclosure builds, the github repo containing panel CAD data was updated accordingly.

Unfortunately, the old Enclosure 1.0 version of the base panel got overridden by the new 3.1 base panel. It would be great if you could stick to the panel_enc2_xxx_size.step naming scheme for the base panel, too. Currently it is named panel_base_size_3.1.step which is kind of misleading.

This would reduce confusion and show users directly, that they need to check the revision history for the corresponding enc1.0 file.