move core_msgs and frontend_utils

[yunzc]

Since PointCloudMapper depends on core_msgs and frontend_utils, I think it should be moved to the common pkg. Let me know what you guys think. See https://github.com/NeBula-Autonomy/common_nebula_slam/pull/1

[BenjaminMorrell]

I am less up to speed on the different packages - so am happy for @femust to make the decision. I think we can eventually remove that package to be honest. Do you use it in LAMP at all @yunzc ?

[yunzc]

Yeah @BenjaminMorrell PointCloudMapper is also used in LAMP. So right now LOCUS is needed to compile LAMP, which is why I would like to move it to common_nebula_slam

[BenjaminMorrell]

Ah, we should definitely move it to common then.

[femust]

ok let's merge this guys :)