Navigation improvements

[rchlfryn]

• We should sort the pages/posts/built-in pages when selecting
• If I add a menu item with sub items, I dont want to have to assign a page or URL
• Bug: if you create a page through the navigation, you don't need to add a layout
• Make donation enable option the same as the rest of the navigation

[rustynwac]

@rchlfryn tech debt or new center onboarding or just a general enhancement we should consider?