Add Qt module dependencies to the IMPORTED targets.

This means for example, that consumers can use:

 target_link_libraries(foo ${QT_QTGUI_LIBRARIES})

instead of also needing to specify all 'public' dependencies:

 target_link_libraries(foo ${QT_QTGUI_LIBRARIES} ${QT_QTCORE_LIBRARIES} )

when using the IMPORTED targets.
Merge topic 'qt4-target-depends' into next

0f9f684 Add Qt module dependencies to the IMPORTED targets.