- Different libraries should have different EXPORTs, so that
you can IMPORT one while building the other. Reported (and
kindly explained) by Kevin Kofler.
- Stick to one header file, though.
While here, update copyright on file.
- The scattering of DLL export macro's is kind of useless;
there are several headers, and then the export macro isn't
even applied consistently. Just drop the one for UI exports,
which was only used in libcalamaresui.
