* update documentation to match latest reality
* check copyright data
* add GPL headers to files as appropriate
* Consider removing "documentation" for methods like ImageElm, IsSolvableGroup
  or at least rewrite it to make clear that what Polenta does
  is providing a new *method* for these, but that the functions
  themselves are part of GAP...
* Implement IsTriangularizableMatGroup for FFE groups?
