Component.queryAll() shall return Iterable<Component> instead of List<Component> for better performance

In other words, queryAll shall not tranverse the whole component tree, until the caller iterates throught the returned collection. Thus, it can be used to implement filter and other function effectively. For example,

for (Component c in comp.queryAll("textbox"))
  if (matches(c)) {
    //do something
    break; //strop the tree  traversal.
  }