Made primitive_extractor templatized with respect to point cloud type and changed parameters

This is in response to https://github.com/strands-project/strands_tabletop_perception/issues/27, so it basically makes it possibly to process pointclouds without colour information. Some of the parameters are also changed to make the extraction run faster, there is still room for improvements though.

Another addition is the subsampling through an octomap before processing. This makes sense as it enables us to define the resolution ourselves which makes it possible to process clouds from different inputs.