Convert all link handlers to use real entities.

Following #1172970: provide a unified way to retrieve result entities

Should we do in views_handler_field_taxonomy, something like this?

  function render_link($data, $values) {
    $tid = $this->get_value($values, 'tid');
    if (!empty($this->options['link_to_taxonomy']) && !empty($tid) && $data !== NULL && $data !== '') {
      $term = taxonomy_term_load($tid); // <-- Load the entity

instead of the dummy entity?