Implement a graphical appfilter editor

[rektdeckard]

Add a feature that allows creating and editing of appfilter.xml files, using an editable TableView

• Populates table with current filter file components
• Uses ViewModel to stage changes and allow commit/rollback
• Allows editing in-place or to new file
• Allows adding of new items
• Allows merging up multiple filter files, useful for handling icon requests
• Integrates with the other Filter tools, e.g. shares common appfilter.xml with mapper tool