No real changes, just clean up sources by removing trailing spaces from
all the non-generated files.
This should hopefully avoid future commits mixing significant changes
with insignificant whitespace ones.
There are no longer any qt headers included in wx/qt headers.
Applications do not need to link with qt librarys anymore, only wxqt libraries.
wxWindow and derived widgets only contain one pointer to their qtwidget, no longer
carrying both base and derived pointers in parallel as was before.