added center of mass to Panda DH definition (and cleaned it up a bit)

[jenskober]

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In pull request #294 some of the inertia parameters were ported from the matlab version. The center of mass for the links was still missing (without which dynamics calculations will be wrong). I've added them here and also cleaned up the white space a bit.

[jenskober]

@AunSiro Thanks! Indeed, both the marcocognetti and frankaemika DH definition include a static 8th joint for the flange, while here this is rolled into the 7th joint, so the center of mass needs to be updated. The robotics-toolbox uses inertia around center of mass, so indeed only the center of mass changes.

[jenskober]

should now be compatible with the latest version in master

[JeanElsner]

I too was about to suggest the same thing, before I saw your pull request. It would be great to see this merged!