Merge prepare module into welcome, and repurpose it as a req checker.

src/modules/prepare/CMakeLists.txt

src/modules/prepare/module.desc

src/modules/prepare/prepare.conf

src/modules/welcome/CMakeLists.txt

src/modules/welcome/CMakeModules/FindLIBPARTED.cmake

src/modules/welcome/checker/CheckItemWidget.cpp

src/modules/welcome/checker/CheckItemWidget.h

src/modules/welcome/checker/CheckerWidget.cpp

src/modules/welcome/checker/CheckerWidget.h

src/modules/welcome/checker/RequirementsChecker.cpp

src/modules/welcome/checker/RequirementsChecker.h

src/modules/welcome/checker/partman_devices.c

src/modules/welcome/checker/partman_devices.h