Fix Qt5 installation
* src/Makefile.am (EXTRA_DIST): Remove qt.conf * src/inst-pinentry.nsi: Fix check for qt section. * src/qt.conf: Removed. Not neccessary anmyore. * src/inst-qtbase.nsi: Install Qt5Widgets. Remove image plugins. Fix platform plugin path. * src/uninst-qtbase.nsi: Update accordingly.
Imageformat plugins should be readded if we are sure that
we need them.