Bug fixes

• #3023023: Include Sentry browser javascript source map file
• Add documentation for hook_raven_options_alter().
• Upgrade @sentry/browser to version 4.5.0

- Code optimization and refactoring w/ dependency injection, compliance with Drupal coding standards.

Scrollup positioning scroll button on bottom and Speed of the scrolling.
Theme visibility of Scrollup button & Background color and hover of the scroll button.

• Issue #2997564: README missing by Vansh983, alonaoneill
• Issue #3015181: Digest interval action does not allow adding email flag by kevin.dutra

Changes from beta4:
- introduces Gutenberg Cloud submodule
- custom block should be now registered using Drupal libraries
- use of hook_gutenberg_blocks_alter() hook is now deprecated
- various bugfixes