during some rework ( not sure if it was me or not ) we try to register
ControlContainerBase on construction as a XModifyListener ( but it's not ). Patch
make ControlContainerBase implement XModifyListener now. iirc the code in question
was moved from UnoDialogControl at some stage and it appears some balls were
dropped :-)

Change-Id: Ifc7084bd7260ceb06334117582facb95bafb6fed