Steps towards using LocalIntegralEnergy instead of problem-specific energy classes

dune/gfe/assemblers/CMakeLists.txt

 #install headers
 install(FILES
-        chiralskyrmionenergy.hh
         cosseratenergystiffness.hh
         cosseratrodenergy.hh
         geodesicfeassembler.hh
         geodesicfeassemblerwrapper.hh
-        harmonicenergy.hh
         l2distancesquaredenergy.hh
         localenergy.hh
         localfirstordermodel.hh