Remove Rules as a dependency

Problem/Motivation

Some projects might not require to use Rules because it is an overkill for this their scopes, but this module require rules.

Rules is not necessary at all since a external module can still do something like:

// Send a tweet.
$twitterPost = \Drupal::service('plugin.network.manager')->createInstance('social_post_twitter');
$twitterEntity = \Drupal::entityTypeManager()->getStorage('social_post_twitter_user');
$accounts = $twitterEntity->loadByProperties([
  'uid' => 1,
]);
foreach ($accounts as $account) {
      $twitterPost->doPost($account->getAccessToken(), $account->getAccessTokenSecret(), "my tweet");
}

Proposed resolution

Remove Rules as a dependency for the module and make it recommended in documentation.

Remaining tasks

Remove dependency
Update project page
Update documentation