message: emit StructureElement.Location in BondIterator.fromStructure
  simpler to handle in themes
diff: */
  import { BondType } from '../../../../mol-model/structure/model/types';
  -import { Unit, StructureElement, Structure, Bond } from '../../../../mol-model/structure';
  +import { Unit, StructureElement, Structure } from '../../../../mol-model/structure';
  import { ParamDefinition as PD } from '../../../../mol-util/param-definition';
  import { LocationIterator } from '../../../../mol-geo/util/location-iterator';
  import { StructureGroup } from '../../units-visual';
  @@ -42,13 +42,11 @@ export namespace BondIterator {
  export function fromStructure(structure: Structure): LocationIterator {
  const groupCount = structure.interUnitBonds.edgeCount
  const instanceCount = 1
  - const location = Bond.Location()
  + const location = StructureElement.Location.create()
  const getLocation = (groupIndex: number) => {
  const bond = structure.interUnitBonds.edges[groupIndex]
  - location.aUnit = bond.unitA
  - location.aIndex = bond.indexA as StructureElement.UnitIndex
  - location.bUnit = bond.unitB
  - location.bIndex = bond.indexB as StructureElement.UnitIndex
  + location.unit = bond.unitA
  + location.element = bond.unitA.elements[bond.indexA]
  return location
  }
  return LocationIterator(groupCount, instanceCount, getLocation, true)
  