WIP: fix rotated inertia

[eric-heiden]

This PR fixes a bug when applying a rotation to inertia matrices defined in the URDF file. WIP on correcting the floating-base case for the ant leg.

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[eric-heiden]

@googlebot I signed it!

[erwincoumans]

Thanks a lot Eric. It looks like the new tests don't pass in CI?

[eric-heiden]

I forgot to commit my changes to test_rbdl so that a random base transform is only set for the tests of floating-base and not fixed-base systems.

[erwincoumans]

Thanks for the contribution, LGTM.