Missing dependencies

[miguelprada]

I noticed some of the packages in this repo do not declare some of their direct dependencies in their manifests, e.g.:

• kdl_conversions requires cpp_common
• tf requires tf2 (also related)
• tf_conversions requires rospy and numpy

Is this deliberate or is it just an omission? I guess it all just works because the dependencies are somehow pulled transitively, which is fine for indirect dependencies, but shouldn't this be avoided for direct ones?