Sidebar improvements
This MR adds two changes to the sidebar:
- Tags are now presented as a Flow of toggleable tag components, bringing them more visually in line with tags elsewhere in Kalendar + also saving vertical space in the sidebar
- The Tags and Calendars sections of the sidebar are now collapsible, with the state saved in the config
- The searchbar for the tasks view has been removed from the filter header and moved to the sidebar (where eventually it will be permanent in views besides the task view), finally making better use of this space and significantly simplifying the filter header (+ also letting us show additional types of info here)
(See collapsed Calendars section, active searchbar, and toggled tag)