close #5751

Prevent 'Object configuration must be an array containing a "class" element.' error.

Fixes #5587: `json_encode` is now used with `JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE` where it makes sense, also it is now default for `Json::encode()`

to avoid issues about 404 links in the guide

make sure to not confuse extending of helper classes with extensions.
Use "customizing" in this case and added note about when this should be done.

fixes #5580

Fixes #5528: added auto_reload to default twig config in both extension readme and template engines chapter in docs

Shouldn't stability=dev be removed?

changed  $query->from(['author' => 'users'])  to  $query->from(['author' , 'users']) on line 354

close #5527

Possible typo.

close #5526