Deprecate RealTime animation mode

The 'RealTime' animation mode is deprecated and will be removed in a future release.
This is necessary because:
 - ParaView does not aim do be a video editor.
 - ParaView processes data and takes the time it needs so real time is really unlikely to happen as expected.

see also https://discourse.paraview.org/t/paraview-time-refactoring/5506/6
