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
Fixed examples to use Qt4 or Qt5 depending on user preference

Change-Id: Ieb302552284d52ed61a4f552ec4526c176392af8
Fixed ParaView macros to use both Qt4 and Qt5

Change-Id: I595069f00809082e30770e0c3e2dcd14ef8f69ae
Reverted macros to use both Qt4 and Qt5

Change-Id: Ibf7b9d492b170232d3f5649ac6a0a14f4da95dd4
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