Added a new ParaViewQt.cmake that provides new macros to find
appropriate version of Qt with relevant components. Instead of checking
which Qt version to use everytime before making Qt macro calls, we now
use macros in ParaViewQt.cmake.

Furthermore, we use the VTK module system to pass information about
which Qt5 version to use (we're not doing the same for Qt4 yet). This
avoids having any extra crud in ParaViewConfig.cmake or
UseParaView.cmake to find Qt5 explicitly.