Fix also an issue on Windows, when using the footprint viewer or the component viewer in modal mode:
Reason: these frames (when run under the Kicad manager) have the Kicad manager as parent, and were built with wxFRAME_FLOAT_ON_PARENT style.
On windows, when the frame with style wxFRAME_FLOAT_ON_PARENT is displayed its parent frame is brought to the foreground, on the top of the calling frame.
and stays displayed when closing the frame in modal mode.
This issue does not happen on unix so we use now wxSTAY_ON_TOP on Windows, and wxFRAME_FLOAT_ON_PARENT on unix to simulate a dialog called by ShowModal.
This is not perfect, but at least it works.
Pcbnew: Code cleaning and bug fix in autoplace functions
Dialog exchange footprints has now a separate button to update the .cmp file, only on request.