Initially Qt5 modifier handling was broken. Therefore a workaround was introduced.
This workaround broke the LyX modifier handling with swap of Command-Control-key disabled.
The change disables the hack to get the correct behavior in LyX.
In particular, the directory frontends/qt4 is renamed to frontends/qt.
Many configurations file have to be updated. All mentions of qt4 in
the source have been audited, and changed to qt if necessary.
The only part that has not been updated is the CMake build system.
