This important part is the last point, the rest is what is needed to
make it happen.
* implement (FindAndReplace|FindAndReplaceWidget)::hasWorkArea, that
tell whether a work area is own by the advanced find & replace
widget.
* factor out method find() from GuiView::findOrBuild.
* implement GuiView::hasVisibleWorkArea, that tells whether a workarea
is visible in the view (current tab in a split or adv. f&r
workarea).
* Finally, in TocWidget::sendDispatch, change the current workarea
temporarily to the document workarea before dispatching the
function. The code tries to be as careful as possible to handle all
cases. The future will tell whether it is good enough.
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.
