Tweak verbiage for pinning/un-pinning from App Library

[jacobgkau]

In the App Library (Applications menu), if I right-click on an icon that is pinned to the dock, I see different verbiage based on whether I'm on 21.10 or 22.04:

• 21.10: Remove from Favorites - fairly clear, but we don't refer to the dock as "Favorites" anywhere else
• 22.04: Unpin - unclear what this does in the context of the App Library

Similarly, there is different verbiage for pinning a non-pinned item to the dock:

• 21.10: Add to Favorites
• 22.04: Pin to Dash

To clarify further over what 21.10 had, I would recommend we make these items refer to the dock instead of the dash/favorites:

• Pinned item: Remove from Dock or Unpin from Dock
• Unpinned item: Add to Dock or Pin to Dock