Set immediate mode rendering to on for STP generated scripts.

By default VTK uses display lists. For HPC runs where we do
a lot of renderings display lists can cause memory fragmentation
which can cause memory issues. So for STP generated scripts
we use immediate mode rendering.
Merge remote-tracking branch 'origin/stp_use_immediate_mode_rendering' into uvcdat-master

* origin/stp_use_immediate_mode_rendering:
  Set immediate mode rendering to on for STP generated scripts.