Fixed default quota field on user management page

Fix default quota settings field
    
The default quota settings field is initially hidden which makes it impossible for singleSelect() to make its width measurements.
    
This fix uses the app navigation slide "show" event to defer the singleSelect() initialization on the default quota field.

To make this work, the app slide toggle was changed to trigger "show" and "hide" events when slid.

Fixes #10178 

Please review @blizzz @MorrisJobke @raghunayyar @jancborchardt 
ouiii spaces not tabs :bomb: