paragraphs 8.x-1.0-rc4

Marking rc4 support.

Changes/fixes compared to alpha2:
#2414839: Make dropdown button the default add mode
#2414679: Make paragraph type visible when editing it
#2414885: Allow adding new form mode
#2414861: Remove repeating "Paragraph" output
#2425035: Add test coverage
#2444345: Test failures
#2427977: Demo module for paragraphs
#2430203: Provide config schema
#2460039: Fix text failure ( Required alt text)
#2445077: Provide CSS for demo module
#2462819: Paragraph demo module is broken
#2467475: Fix the tests after form fields were renamed
#2448619: Translate paragraph types broken
#2469997: Creating a new paragraphed article is broken
#2470773: Replace all occurrences of old classes with their new equivalent
#2414913: Support entity translation of paragraphs
#2463491: Hide add/remove buttons when translating
#2473721: Check multilingual settings for paragraphs
#2478691: Test coverage for the "Add mode" setting (dropdown/list)
#2490586: Use EntityChangedTrait for paragraphs
#2485547: Add config_export to ParagraphsType ConfigEntityType annotation
#2433099: Provide a custom diff plugin
#2429273: Test coverage for the "Edit mode" widget setting
#2506497: Wrong module group of demo
#2503767: Missing title for edit paragraph type page
#2429277: Test coverage for revisions
#2503801: Setting a help text for a paragraph field is broken
#2530044: Edit widget test is failing
#2461689: demo module: Multilingual setup
#2532756: Support nested paragraphs
#2562547: Fix test that rely on local tasks and actions
#2582961: Broken in Drupal 8 RC1
#2513226: Populate new translation with data from original
#2584865: Remove entity_reference from paragraphs_demo.info.yml
#2601126: Update tests with date in file url
#2569483: Add nested paragraphs to paragraphs_demo
#2527644: Test coverage for editing a translation
#2608090: Replace !placeholders
#2614902: AJAX Response: The database connection is not serializable
#2615746: Typo in InlineWidget help text
Fix styling, class of widget changed
Fix wrong js load, we dont have this file
Add default entity reference revision settings
Fix tripple saving of entities
Fix dropdown button
Add collapse button for preview mode