New features

- Adds Drupal 9 support
- Adds Gutenberg 8.x support

Github milestone: 8.x-1.6

- [#228] Added revenue reports for prepaid and postpaid users.
- [#235] Fixed an issue with plans page not updating after purchasing a plan

Drupal 9 compatibility

Improvements integration from feature request #3139257 by hatuhay:
extra permissions, page rendering inside theme, select options for full screen or framed layout, log events;
Other improvements:new display layout, option to set windows size, side menu to access video settings, user avatar inserted;
Added help section;
Added install file;

* Drupal 9 compatibility
* Minor fixes

* PHP 7.3 compatibility