Use info sidebar for desktop instead of drawer, make actions for adding and removing tags more distinct, change tag appearance
Changes:
- Desktop now uses a sidebar with a movable splitter instead of a drawer. Did not use SplitView, because it's just not very usable. It seems like it'll be better in Qt 6.
- Tags now have a pointy shape and they only have buttons for removing them.
- Tags are now added via a combobox that is always visible. You can click on the down arrow to see a list of existing tags that have not been applied to the current image.
