Add analysis tools / prototypes

[hamogu]

MARXS results are a simple Table of photon properties. That's all we get from a raw detector read - out (or, actually, a lot more, since the MARXS tables has all sorts of columns a real table would not have).
However, this would be a lot more useful if MARXS provided tools to analyze this a little. For example, adding te right keywords to make DS9 display the event list would make it easier to look at it, a way to generate RMFs and ARFs would make it much easier to simulate spectral missions etc.

Much of this will be mission specific (there is a reason that CIAO and SAS are huge software packages), but if MARXS could have some simple functions or at least ways to make it easier to write those functions for new instruments that would help.