[TASK] Remove the recalling of the indexAction, because it is not needed anymore with the languagevisibility changes

[BUGFIX] Fix totally broken page browser implementation, Cleanup code / Remove dead code / Fix potential error cases

update documentation, add example on how to add multiple news feeds with different configurations (different content per feed).

- Group by Tags: Not respecting the rootline, if the option onlyNewsWithinThisPageSection is true.
- Group by Categories: Not resprecting the rootline, if the option onlyNewsWithinThisPageSection is true. Also not respecting the multi language behaviour of the TYPO3 9 pages table.
- No grouping:  Not respecting the rootline, if the option onlyNewsWithinThisPageSection is true.

[BUGFIX] Fix the selection of news by category if categories are translated but news are just set to "force" by languagevisibility

flexform config for all plugins

Integrate a general function into the AbstractController to
handle offset calculation for the pagination.

Alterring GET parameters should never be done. Instead using method
parameters to alter functionality.
This fixes side effects on the canonical URL generation, if the news
plugin is present with one of the list-Actions assigned.