Wip overlay position from right

Thats a manual merge of my pull request #891 from last year.

Added "right" as a setting for the position of the Overlay.

I needed the overlay to stick to the right side of the window for all screensizes and on horizontal scrolling.

```
works like the "left"-setting but:
    * has no 'center' (unneeded - use left:'center' instead
    * defaults to false (unused), is only used if a pixel or % value is set
    * if left and right are set, left will be ignored
```