Fetches a specific URL alias from the database.
$conditions: An array of query conditions.
FALSE if no alias was found or an associative array containing the following keys:
public function load($conditions) {
  $select = $this->connection
    ->select('url_alias');
  foreach ($conditions as $field => $value) {
    $select
      ->condition($field, $value);
  }
  return $select
    ->fields('url_alias')
    ->execute()
    ->fetchAssoc();
}