QmlDesigner.PropertyEditor:  Fix echo mode

TextEdit does not have an echoMode property
and for TextField it has to be an integer.

Task-number: QTCREATORBUG-11136
Change-Id: Ib560dd18ed31f9a735fd2c6874334e1479fd3a31
Reviewed-by: Marco Bubke <marco.bubke@digia.com>