Before this change, the filter button on the top right was positioned using absolute positioning and plenty of tricks, which were brittle and not really maintainable. Now, the buttons are positioned using flexbox, which should make this a lot more maintainable.
Previously, the actual filter was kept as-is when sending it to the api, essentially creating an invalid filter. This change fixes this, transforming the filter before saving and after loading.
Resolves https://kolaente.dev/vikunja/vikunja/issues/2233