WIP: new transfinite algorithm for nicer meshes of 3-sided surfaces

New transfinite algorithm from @ermakov for nicer meshes of 3-sided surfaces; initial implementation (#1094 (closed))

IMO before merging in master we should remove the significant amount of duplicate code between the two paths (transfinite_standard true or false), and probably add an option to restore the old behavior if needed (i.e. to force transfinite_standard to true).