kcm/keyboard: Search/Filter and DelegateChooser for xkboptions tree
Search
Search will help the user navigate through the tree items faster. All thanks to @ratijas for the implementation of this feature.
DelegateChooser
Instead of a checkbox that showed whether any items were selected for this group, bold text is set for the group title so that the user is not misled when he tries to change the state of this checkbox.
I use RadioButton for groups that are exclusive so that the user understands that only one item can be selected in this group.