message: use MOL (not UNK) as name for unknown ligand molecules
  UNK is for unknown amino acids in CCD
diff: /**
  * Copyright (c) 2019-2020 mol* contributors, licensed under MIT, See LICENSE file for more info.
  *
  + * @author David Sehnal <david.sehnal@gmail.com>
  * @author Alexander Rose <alexander.rose@weirdbyte.de>
  */
  @@ -19,7 +20,7 @@ import { IndexPairBonds } from './property/bonds/index-pair';
  async function getModels(mol: MolFile, ctx: RuntimeContext): Promise<Model[]> {
  const { atoms, bonds } = mol;
  - const UNK = Column.ofConst('UNK', mol.atoms.count, Column.Schema.str);
  + const MOL = Column.ofConst('MOL', mol.atoms.count, Column.Schema.str);
  const A = Column.ofConst('A', mol.atoms.count, Column.Schema.str);
  const type_symbol = Column.asArrayColumn(atoms.type_symbol);
  const seq_id = Column.ofConst(1, atoms.count, Column.Schema.int);
  @@ -27,7 +28,7 @@ async function getModels(mol: MolFile, ctx: RuntimeContext): Promise<Model[]> {
  const atom_site = Table.ofPartialColumns(BasicSchema.atom_site, {
  auth_asym_id: A,
  auth_atom_id: type_symbol,
  - auth_comp_id: UNK,
  + auth_comp_id: MOL,
  auth_seq_id: seq_id,
  Cartn_x: Column.asArrayColumn(atoms.x, Float32Array),
  Cartn_y: Column.asArrayColumn(atoms.y, Float32Array),
  @@ -36,7 +37,7 @@ async function getModels(mol: MolFile, ctx: RuntimeContext): Promise<Model[]> {
  label_asym_id: A,
  label_atom_id: type_symbol,
  - label_comp_id: UNK,
  + label_comp_id: MOL,
  label_seq_id: seq_id,
  label_entity_id: Column.ofConst('1', atoms.count, Column.Schema.str),
  @@ -47,12 +48,12 @@ async function getModels(mol: MolFile, ctx: RuntimeContext): Promise<Model[]> {
  }, atoms.count);
  const entityBuilder = new EntityBuilder()
  - entityBuilder.setNames([['UNK', 'Unknown Entity']])
  - entityBuilder.getEntityId('UNK', MoleculeType.Unknown, 'A');
  + entityBuilder.setNames([['MOL', 'Unknown Entity']])
  + entityBuilder.getEntityId('MOL', MoleculeType.Unknown, 'A');
  const componentBuilder = new ComponentBuilder(seq_id, type_symbol);
  - componentBuilder.setNames([['UNK', 'Unknown Residue']])
  - componentBuilder.add('UNK', 0);
  + componentBuilder.setNames([['MOL', 'Unknown Molecule']])
  + componentBuilder.add('MOL', 0);
  const basics = createBasic({
  entity: entityBuilder.getEntityTable(),
  