Implement Nudge from Bottom / Right

[nikosdion]

The nudge values are currently only ever set from the Top or Left edge.

We could have a dropdown to select Top/Bottom and Left/Right, changing the nudge labels accordingly.

The implementation is fairly straightforward.

Nudge from Bottom can be converted to a nudge from top value by doing image height - text box height - nudge from bottom.

Nudge from Right can be converted to a nudge from left value by doing image width - text box width - nudge from right.

This way we can leave our implementations as they are, adding the minimal code required to convert the bottom/right nudge values into their equivalent top/left values.