Feature request: Possibility to specify the position of the validator in the popup mode

[OndrejUzovic]

Sometimes, e.g. if it is a last line of a section, it is difficult (or waste of space) to provide an extra space to display the popup validator on the bottom side.

Therefore it would be nice to have a possibility to specify if the side the popup validator shall be displayed on. It means, to specify if it shall be displayed on top, bottom, right or left side.