* Refactor OPML export categories
Simplify code to comply with types hints.
And renamed a property to plural.
* Automatic simplification of layout for many feeds
New advanced property to automatically simplify the layout when there are many (1k+) feeds so that FreshRSS works out of the box with 20k+ feeds scenarios https://github.com/FreshRSS/FreshRSS/pull/4347
Merge https://github.com/FreshRSS/FreshRSS/pull/4356 first.