Summary

This PR can be summarized in the following changelog entry:

• Added filters for the Breadcrumb and WebPage Graphs.

Relevant technical choices:

• Added selection creation helper.
• 3 choices: Don't influence, Always include and Never include.

Test instructions

This PR can be tested by following these steps:

• Switch to this branch.
• Activate the plugin in WP.
• Go to the Tools -> Yoast Test page.

• Go to a WP output post/page/whatever, open the source and copy the JSON+LD script.
• Use Google's SDTT to test the stitching.
• Try different values and check if the schema output matches.
  • Don't influence should result in the same output as without the plugin installed.
  • Always include is a bit harder to verify with some options. But you can go to SEO -> Search Appearance -> Breadcrumbs and disable the breadcrumbs output. Note this is now not stitched anymore due to not being linked in the webpage.
  • Never include will also result in strange stitch situations.

Quality assurance

• I have tested this code to the best of my abilities
• I have added unittests to verify the code works as intended

Fixes #35