* [not-working] add a gz-omnicopter model
* Fix axis directions on omnicopter model
The omnicopter joint axis directions had to be adapted for sdf 1.9 as it has different conventions for joint axis definitions.
* include model from gz-fuel & remove mesh files
* Fix omnicopter model using fuel
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Co-authored-by: Jaeyoung Lim <jalim@ethz.ch>
