removal of nodes, undo/redo, twins, lines with intersections, layout fixes, interface fixes
fix broken undo due to incorrect affected node list returned by LineSet
fix line crosings, fix some multi-rank edge layouts, fix some sharp corners, fix twin properties
fix disorder loading/restoring
Merge branch 'feature-pedigree-layout-beta' of https://github.com/phenotips/phenotips into feature-pedigree-layout-beta