ColumnChooser - Drag&Drop problem with special Characters and QT 4.6.8

... the .toUTF8() conversion used with QT5.3.x to handle special
characters (e.g. german Umlaute) in column chooser does not work for QT
4.8.6 (at least not for the Windows) - as a result (Drag&Drop from those
fields into Columns or Search Field is not working)
... following the approach other places, changed approach to
"serialization" of the info for "Drag&Drop" - so work independent on any
QT conversions (which seem to depend on other conditions - change over
time)
Merge pull request #981 from Joern-R/pull4

ColumnChooser - Drag&Drop problem with special Characters and QT 4.6.8