[shortcuts][pref] Create ability to Add or Remove Shortcuts using Preferences window

[DamianSuess]

As a user, I want to be able to easily add/remove shortcut add-in items using the TreeView editor in the Preferences dialog.

Acceptance

• Add items to GUI editor
• Remove items from GUI editor
• Save editor results to JSON

Out of Scope

• Editing JSON data (text and targets)
• Moving items via drag-drop