thunder 8.x-1.0-rc3

Test improvements
- Added tests for SEO functionality (Metatag, Sitemap)
- Code style tests and fixes
- Update tests to work with current module markup

Config changes
- Activated revisions for article and basic page
- Media URLs are required for twitter and instagram entities
- UX: better responsiveness on content list
- Improve image style for media thumbnails
- UX: Add author filter to content overview
- UX: Add sorting to entity browser views
- Enable auto select on multiple_image_browser
- Reorganize node and term edit pages
- Auto open media browser
- reduce allowed allowed upload extensions in image browser
- Label form element non-required in the entity form
- Change gallery paragraph to simple widget
- Use responsive images in gallery

Fixes
- Fix entity browser preselection after error
- Add missing svg files for entity browser
- UX dropzone: #2696915: Checkmark indicator for upload screen
- UX dropzone: #2633346: Implement maxFiles
- UX dropzone: #2823670: Improved MultiStep selection display (DropZone Widget)
- Fix term access for unpublished terms
- UX media browser: #2778305: Open entity browser with one click from Entity Browser IEF widget
- #2807735: Make posts responsive
- Fix PHP Notice
- Better entity browser usability on mobile devices