Restore Qt4 and enable option to build against Qt5

Added a new flag called PARAVIEW_QT_VERSION that can be set to either 4 or 5.
Depending on the value of this flag, the appropriate Qt version is looked for
and built against.

If PARAVIEW_QT_VERSION==5, the necessary Qt5 modules can be
imported by including the script "ParaViewQt5.cmake". This script also sets
important Qt variables used throughout the project.

Setting the officially supported version of Qt5 to 5.0.2. Although, paraview
compiles fine against Qt-5.0.0, there are known issues that prevent it from
being fully functional (https://bugreports.qt-project.org/browse/QTBUG-28872).
Setting the minimum Qt5 version to 5.0.0.

Change-Id: If3cb97ff798b22a5fb4e89c0be948ca6b65ee1d1
Compile Flags to

Change-Id: If6482e8f51c4e4e7e61f702e7c33bedc04108d66
Modified ParaView macros to use both Qt4 and Qt5

Depending on the PARAVIEW_QT_VERSION variable value, the appropriate Qt version
is used.
Change-Id: I595069f00809082e30770e0c3e2dcd14ef8f69ae
Compile Flags

Change-Id: Ib717cf7dcb3d05eed452b7e07b2988909c45a035
Import Qt5Widgets module at the top level

This ensures all the required Qt5 variables can be found.
For example, just importing Qt5Core does not help find QT_UIC_EXECUTABLE using
the macro "get_target_property(QT_UIC_EXECUTABLE Qt5::uic LOCATION)". This must
be a Qt5 bug.

Change-Id: Ie6f4a708682ad8cf2391d218c193d8127e4c44f7