Rework fsutils class to only use Qt-style separators

  fsutils methods are guaranteed to accept strings with both native and qt-style separators and return strings with qt-style separators where appropriate
Modify configure script to support both Qt4 and Qt5 (also modify qconf project and modules to produce such script).
Add QHttp* classes dropped in Qt5.
Update QtSingleApplication.
Fix functions and macros using to support both Qt4 and Qt5.
Fix translations bundled with Qt.