Add event to denied action

Let plugins modify the text displayed on the denied page

fix handling of loading auth backend

When a non existing auth backend was configured, the action router ran
into an infinie loop exception. The reason was that the denied action
required a configure

fix handling of loading auth backend

When a non existing auth backend was configured, the action router ran
into an infinie loop exception. The reason was that the denied action
required a configured auth system, but denying access should always
work.

Interestingly the problem did not occur when the auth backend signalled
a failure to load. This was because the auth backend was not properly
deinitialized. This is now done.

To aid debugging similar problems, fatal errors are now logged through
the logging mechanism in the action router

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check CSRF token in draftdel action. fixes #3563

check security token on logout. fixes #3561

Fix various errors in PHPUnit tests on PHP 8

minor cleanup in AdminAction

removed unecessary method, added doc blocks

Ui\Diff hierarchy

move Ui\Diff to Ui\PageDiff

create Ui\PageRevisions class

new Ui\PageRevisons is dedicated for page revisions

stricter user check in AbstractUserAction

Allow revert action for logged in users only

This should prevent accidental reverts by bots on open wikis

re-declare deprecated functions for backward compatibility

`dbg_deprecated()` is called in `html_diff_head()`, `html_diff_navigation()`, `html_diff_navigationlink()`, and following functions:

* `h

re-declare deprecated functions for backward compatibility

`dbg_deprecated()` is called in `html_diff_head()`, `html_diff_navigation()`, `html_diff_navigationlink()`, and following functions:

* `html_denied()` is not used any plugins, but added fallback just in case.
* `html_locked()` is used by one third-party plugin (AjaxEdit), fallback should be added.
* `html_insert_softbreaks()` is used by one third-party plugin (TOS, terms of service), fallback should be added.

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use $INPUT instead of $_SERVER

Ui\Subscribe class replaces tpl_subscribe()

use "difftype" in Ui\Diff

create constructor of Ui\(Recent, Revisions)

create constructor of Ui\Index class

call Ui\Diff from Ui\(Conflict, Draft)

define constructor of Ui classes

create Ui\ConflictForm

Remove Ui\{Denide, Locked} class

They are not UI components. We should show error message in Action\{Denide, Locked}::tplContent() methods.

Ui\PageView class replaces html_showf)

Ui\Diff class replaces html_diff()

Ui\Diff()::diffNavigation() still uses Doku_Form class, Further work needed!

Ui\Revisions class replaces html_revisions()

no space between printed items such as date, unsername, sizechange info. Further work needed for better looks/design.
The code for page navigation in Ui\

Ui\Revisions class replaces html_revisions()

no space between printed items such as date, unsername, sizechange info. Further work needed for better looks/design.
The code for page navigation in Ui\Revisions is different with Ui\Recent.

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Ui\Recent class replaces html_recent()

no space between printed items such as date, unsername, sizechange info. Further work needed for better looks/design.