fix Kwf_Form_Field_ImageViewer

was completely broken.
TODO: don't use fixed preview size
ShowSelect implemented

shows the value from a Field_Select
fix toStringField

that is the right way to do that
prevent error if field is not set
add version to generated setup.php

fixes issues when incompatible changes are made to generated setup.php
(especially when changing branches in kwf)
Merge branch '3.1' into 3.2