meumapps-ss app file shuffle, barrier height, and gradient energy coefficients

The bulk of this MR is for the gradient energy coefficients part of #11 (closed). It already has the barrier height calculation done.

To make testing this and the rest of the app code easier, I split the main function into a new file, main.cpp. @4pf, any objections? I also created a new namespace for the meumapps-ss functions and classes. I'm not quite sure of the planned scope of the "SS" class, so for now I left it as is. But it might belong in the MeumappsSS namespace too.

@4pf, I can merge this into master even though the functionality isn't done yet if that makes you life easier in terms of the content of the files being moved around. I'm not sure if git will take care of that automatically in a merge or not.