made the project compatible to dune2.6
made minimal changes to make the projact compatible with the 2.6 release of dune. Due to the use of macros, it should be backwards compatible to 2.5 for now. Changes:
- changed the namespace name istl to ISTL
- changed the usage of referenceElement(geo)
- lifted the c++ standard to c++14
Changed also:
- Added the dune-glio.pc.in and the make/modules/CMakeLists.txt files, since they are essential to build the project
- deleted the config.h file in the main directory, since it should be generated automatically in the build folder