This implementation is based on the implementation in MantidPlot.
A C++-based executor has been added that can execute Python code
with the option of installing a trace function to update
a progress marker on a given editor window.

The old implementation attempted to chunk up the script into
the smallest executable blocks and mark each of these as when
they were executed. There were 2 issues:
  - the chunking of the scripts was error prone as it actually
    requires a good knowledge of how Python internally handles
    indentation etc. It was fairly easy to break and future
    internal updates to Python would have required unknown changes.
  - the progress reporting resolution was far poorer than MantidPlot
    as the actual line being executed was not reported but inferred
    by what block was being executed giving a false sense of progress
    through a script.