Merge pull request #88 from ipa-fxm/hydro_dev

fix xacro:include tag
New stl files for cob4
merge
Merge error
deleted offset
Merge pull request #89 from ipa-nhg/hydro_dev

Stl files for cob4 and defined colors
remove material physic properties of wheels to use default, fixes #90
update cob4_base stl file
Merge pull request #92 from ipa-nhg/hydro_dev

update cob4_base stl file
New maintainer
Merge pull request #93 from ipa-nhg/hydro_dev

New maintainer
Merge pull request #91 from abubeck/hydro_dev

remove material physic properties of wheels to use default, fixes #90