Add possibility to generate raster scan data RST files

[grzanka]

This is not to be confused with reStructured tests.
see https://github.com/pytrip/pytrip/blob/a7583edaa5261ed01a48397cfab7947a5aa5d800/pytrip/raster.py

Master switch want_rst seem to be there:
https://github.com/pytrip/pytrip/blob/a7583edaa5261ed01a48397cfab7947a5aa5d800/pytrip/tripexecuter/plan.py#L134

But we need to check it pytrip fully supports that, see:
https://github.com/pytrip/pytrip/blob/a7583edaa5261ed01a48397cfab7947a5aa5d800/pytrip/tripexecuter/execute.py#L431