message: support setting pdb/emdb provider in viewer index.html
diff: }
  var hideControls = getParam('hide-controls', '[^&]+').trim() === '1';
  + var pdbProvider = getParam('pdb-provider', '[^&]+').trim().toLowerCase();
  + var emdbProvider = getParam('emdb-provider', '[^&]+').trim().toLowerCase();
  var viewer = new molstar.Viewer('app', {
  layoutShowControls: !hideControls,
  viewportShowExpand: false,
  + pdbProvider: pdbProvider || 'pdbe',
  + emdbProvider: emdbProvider || 'pdbe',
  });
  var snapshotId = getParam('snapshot-id', '[^&]+').trim();
  