BUG #13061: Adding ability to build ParaView without WebKit.

Added a new advanced cmake option QT_WIDGETS_DISABLE_QTWEBKIT. That can be used
to disable WebKit support in ParaView. Users can turn it ON to disable the
dependency on QtWebKit.

Change-Id: I0c40dba7f559efd5f39d86c8d7612086381c0272
Merge topic '13061_make_webkit_optional' into next

477d409 BUG #13061: Adding ability to build ParaView without WebKit.