Make Qt examples build with either Qt4 or Qt5.

1) Added conditional instructions to the CMakeList.txt files
    based on VTK_QT_VERSION.
2) Cleaned up the CmakeLists.txt files to make them more consistent.
3) Added QT_VERSION ifdefs, where appropriate, to take into account
    differences between Qt5 and Qt4.

Change-Id: I738a4782dda7ef920d7418918e6ec3938f1c2297
Signed-off-by: Andrew Maclean <andrew.amaclean@gmail.com>
Merge topic 'fix_qt_examples_for_qt5' into master

eeba833c Make Qt examples build with either Qt4 or Qt5.