New package scitos_2d_navigation, this basically just moves our stuff from 3d_mapping to the new structure.

This is just a dummy pull request, essentially it should be for the whole repo.

The package assumes that we have a tf tree running. This should be launched together with more basic tasks. It also doesn't include any launch file for gmapping as it doesn't need any configuring (maybe there is room for some though). Instructions for this are included in the wiki.