- Added `Undo` button and keybind (`CTRL+Z`)
- Added `Redo` button and keybind (`CTRL+Y`).
- Made folder names clearer when added as merge targets
    - They should no longer be paths (e.g. `~wierd-folder/pthname`)
- Added paths are now in a `GridView` for cleaner formatting. The columns may be manually adjusted by the user.
- You can now press `DEL` to delete the current selection.
- The starting help text, shown when no merge targets have been added, is now more prominent.