changefreq implementation missing

Adding patch with all required changes to add changefreq element.

Thanks for your input guys. @vytch Can you incorporate your change into #5? It seems that one is more complete. I am going to review it in a few moments.

@nikunjkotecha thanks for yout patch. I have found a couple of issues that need fixing before we commit.

1. We need an update hook to alter existing data, as the sitemap threw an error when I ran indexation after applying the patch. I believe we need to alter the db schema of simple_sitemap_entity_overrides and configuration storage of simple_sitemap.bundle_settings.* and simple_sitemap.custom.
2. This is probably related, I'm getting Notice: Undefined index: changefreq in Drupal\simple_sitemap\Simplesitemap->setEntityInstanceSettings() (line 418 of Simplesitemap.php). when trying to override entity instance.
3. This is probably also related, when visiting Custom links after applying the patch, the paths are formatted incorrectly in the textbox. There must be an (optional) way of adding changefreq for custom links and the value added needs to be validated.
4. Line 314 of the patch doesn't seem to make sense: + ? $custom_link['path'] . ' ' . $this->formHelper->formatPriority($custom_link['changefreq']). There should be a formatChangefreq function I believe.

Another question is, what do you think about implementing automatic changefreq values for entities (as we have last viewed and created data) as xmlsitemap does?

Thanks!

According to the comment in #9, re-rolled the patch in #5 to fix following:

1. Added update hook to add a column simple_sitemap_entity_overrides to fix the PHP warnings. The config storage is already changed in the patch in #5.
2. Notice: Undefined index: changefreq in Drupal\simple_sitemap\Simplesitemap->setEntityInstanceSettings() (line 418 of Simplesitemap.php). is gone after altered the db.
3. Made changes in helper function to store changefreq for custom links and display changefreq properly in form.
4. No need to use formatChangeFreq formatter as it is just string selected from dropdown list.

Have not got time to think about the automatic changefreq generation yet. The options allows user to control the value per content type is good enough for our project at the moment.

Seems no need to add column in db as the settings are stored as serialised array.

Added update hook to alter all existing data.

Rerolled patch to alter all existing settings.

Thanks for your patches guys, couldn't use them much however. I've committed all changes to dev, please take a look for me.