Implement command bar history

[Delisa]

Add the ability to move back/forward in the list of commands previously used

• Add ivars for history storage to CommandBarDelegate (items, capacity, currentIndex, draft)
• Handle up/down key presses for changing text
• Ensure text changes do not occur during autocompletion/text selection
• Reset index to 0 after executing a command
• Prepend command text to items after executing a command
• Allow scrolling below last command to either empty string or "draft" command
• Truncate items to capacity after prepending commands
• Skip prepending command text if equal to the previous command