Factor out the code that connects to a newly created dialog and then
use that also in GuiGraphics.
There must be many other dialogs that need this same treatment....
In particular, the directory frontends/qt4 is renamed to frontends/qt.
Many configurations file have to be updated. All mentions of qt4 in
the source have been audited, and changed to qt if necessary.
The only part that has not been updated is the CMake build system.
