refactor: Switch search by identifier to use predicates

[mykola-mokhnach]

Internally search by identifier is anyway changed to predicate search. Also, the current implementation might sometimes be confusing, because the value we show in the page source for name is wdName, which is calculated as

  NSString *identifier = self.identifier;
  if (nil != identifier && identifier.length != 0) {
    return identifier;
  }
  NSString *label = self.label;
  return FBTransferEmptyStringToNil(label);

[mykola-mokhnach]

Possibly fixes #408 (comment)