Replace all variable_get/set() calls with the config system

Committed and pushed a first pass to 8.x-4.x

This takes care of all the straight forward ones, there are a handful of trickier ones left, leaving open to finish up those.

Thanks for the patches @bobrov1989!

1. +++ b/config/install/webform.settings.yml
   @@ -33,3 +33,5 @@ allowed_tags:
   +export_path: 'temporary://'
   +table: 0
   

   These also need to be added to webform.schema.yml

2. +++ b/includes/webform.report.inc
   @@ -18,7 +18,7 @@ function webform_results_submissions($node, $user_filter, $pager_count) {
   -  if (!webform_variable_get('webform_table')) {
   +  if (!\Drupal::config('webform.settings')->get('table')) {
   

   The old webform_table variable is going to be removed as we'll be removing support for the old hard coded table listings and only offering their new views equivalents (which is already the default in 7.x-4.x). However I guess that's out of scope for this issue so a simple replacement for now is ok.

3. +++ b/includes/webform.report.inc
   @@ -802,7 +803,7 @@ function webform_results_download_form_submit(&$form, &$form_state) {
   -  return drupal_tempnam(variable_get('webform_export_path', 'temporary://'), 'webform_');
   +  return drupal_tempnam(\Drupal::config('webform.settings')->get('export_path'), 'webform_');
   

   Is temporary:// still the correct default here in D8? I imagine it is but would like to be sure.

4. +++ b/webform.module
   @@ -4415,11 +4403,12 @@ function webform_date_string($array, $type = NULL) {
   -    $format = variable_get('date_format_' . $type_name, 'D, m/d/Y');
   +    $format = $config->get('date_format_' . $type_name) ? $config->get('date_format_' . $type_name) : 'D, m/d/Y';
   

   This is incorrect as before it was looking for the "global" 'date_format_' . $type_name variable yet here you're looking in webform.settings. Additionally I'm guessing the date module's changed the way it stores date formats (i.e. is it actually stored in 'date_format_' . $type_name?) so it will probably need to be adjusted for that.

Committed and pushed to 8.x-4.x.

Thanks for your answers in #10 @bobrov1989.

1. One small issue fixed on commit:

   +++ b/config/install/webform.settings.yml
   @@ -33,3 +33,5 @@ allowed_tags:
   +table: 0
   

   table is a boolean and should default to false (again it will be removed in the near future once views support is ported). This also made me open #2504493: Standardise config types and defaults.

2. +++ b/webform.module
   @@ -4419,7 +4407,7 @@ function webform_date_format($type = NULL, $exclude = array()) {
   -    $format = variable_get('date_format_' . $type_name, 'D, m/d/Y');
   +    $format = \Drupal::config('core.date_format.' . $type_name)->get('pattern') ? \Drupal::config('core.date_format.' . $type_name)->get('pattern') : 'D, m/d/Y';
   

   I can also confirm that \Drupal::config('core.date_format.non_existent_format')->get('pattern') returns NULL, so all good there too.
   I'm a little hesitant to leave the default 'D, m/d/Y' hard coded there, however as it differs from the default 'medium' format I think it's ok to do so.
   Also no need to call config->get twice, instead I just assigned it to a local variable, fixed on commit.