Replaced many instances of t() with $this->t(),

\Drupal::l() with $this->l(),
\Drupal::url() with $this->url(),
\Drupal::logger() with $this->logger(),
\Drupal::entityManager() with $this->entityManager(),
\Drupal::configFactory() with $this->configFactory(), and
\Drupal::moduleHandler() with $this->moduleHandler()