[Hat] Hat-Gui, new tool

[Neil Mitchell]

Hi,

> Great. I wonder whether it would be more sensible if the HatStack itself
> wouldn't do the trace file opening, hence also not get a FilePath as
> argument. In your GUI you want to combine several tools.
I considered that, however some tools are not going to use the
standard Hat library - for example w-hat, and then the person calling
the API will need to know how to open each hat file for each library.
However, I don't mind either way.

Thanks

Neil