Update Geppetto model for c302

[gidili]

Migrate XML version to XMI to work with current version of geppetto.

Fortunately this has been done for the c302 sample (the sample accessible from live.geppetto.org, the actual project is in the core bundle). We basically need to take the Geppetto model for that sample and update the wormsim with the new model abut we need to keep the neuroml we currently have in the wormsim as it has backer names.