#324 Create new dialog control for assign/remove buttons

[Miro Halas]

Double data list consists of two scrollable tabless,
usually one in iframe and second in embedded in the
page with assign/remvoe buttons in between them. The
buttons have to be at this time coded manually. Create
new control dialog:doublelistbuttons which will
automate generation of these buttons so that the
statisc parts do not have to be coded by users.