Make the sidebar's view switching UX more conventional and less buggy
Okular's sidebar vertical view chooser toolbar has a few problems:
- It's a nonstandard UI that most other document readers don't have
- What is shown and what is hidden is simultaneously too configurable while still not offering the desirable UI common to other programs (i.e. no visible category chooser, but a sidebar capable of displaying thumbnails, table of contents, search results, etc.)
- With labels on (by default) it takes up quite a bit of horizontal space, while with labels off, the categories are less than clear
- UX is kind of clunky with nonstandard behaviors (e.g. clicking on the current category to hide that category's view while keeping the view chooser visible, showing mostly-disabled items)
- By default it displays >22px size monochrome icons, which violates the HIG
- It's made with custom painting code, which reduces maintainability and introduces bugs (e.g. https://bugs.kde.org/show_bug.cgi?id=408190)
This patch removes the vertical category chooser entirely and replaces it with a combobox on the top of the sidebar view itself. A button is added to the default toolbar to quickly hide or show the sidebar. This improves the UX, fixes a variety of bugs, and deletes a lot of custom code of dubious long-term maintainability.
This is an alternative to !22.