Cargo pad design tweak

[the_s_guy]

The central asymmetry in the previous design was clever, but it just wouldn't work when the pad was being used sideways - as in the train or wyvern modes. Either the central block is going to be able to have to slide back and forth a little - which means more stablisation issues elsewhere to compensate - or it's going to have to be able to rise and fall a little, which means designing a teeny-tiny springloaded connector.

Dammit.