Implement mdvseg leaflet segmentation as segmenter

[BartBruininks]

Create the input options for proper leaflet segmentation for non-PBC labeling. This will allow for completion of self touching vesicles. Currenly we are just using the labels from the clustering and then perform density based segmentation for each label. However, this does not work well for lipids, for they can touch but not fuse. We would like to perform the leaflet segmentation inside mdvwhole. This should fix Melanie's issues and also Peter Park's system would benefit from this. I think this is not cheating as this is a energetically well separated state from fused leaflets. Maybe we should allow for reading a selections.inp and an mdvseg.inp.