qgisimporter - Determine vector data type using OGR

Probably not the better approach to dive into GDAL/OGR code, but this
should do the job as for now. Note: GDAL2 unifies the API between vector
/ raster code, so this is already deprecated, but debian sid still
provides me a < 2.0 version.

Let's see that later. Another note: probably, there is some code in
Mapserver doing basically the same thing, see if I cannot reuse it.
QUndoStack - Whole app shall use the same QUndoStack ?

Mapsettings and mainwindow are now sharing the same QUndoStack. Not sure
of the approach, but allows for now to have a more "graphical" insight
of what is going on.
layerSetting QDialog should be modal
Add buttons and make windows modal