make it clearer that DbGridControl_Base::RemoveColumn
is meant to be called unconditionally

 * Added variable initializations when reading from SvStream
 * Minor code cleanups
 * Translated some German comments

Changes related to an issue showing in Valgrind over a misformed WMF and
EMF

Signed-off-by: Tomáš Chvátal <tchvatal@suse.cz>

otherwise calling delete on a base class pointer to an instantiation of a
derived class doesn't call the derived class's dtor