Fix LXQT-9999 Build Failures

* lxqt now requires qtmimetypes library to compile
* New Ebuild for qtmimetypes
* Patch for build failures in lxqt-config
* Add dependency qtmimetypes use flag in libqtxdg in order to build
  liblxqt and lxqt-panel packages
  Note: razor-qt does not require the qtmimetypes use flag (yet)
It uses Qt5 Mimetypes API when qt5 flag is set, right? In this case you should prevent dependency on x11-misc/xdg-utils if qt5 USE is set. Also you should make USE qtmimetypes be available only if qt4 USE is set.