Merge branch 'fix/PYTHONLIBS' into 'master'

Cmake: Look for PYTHONLIBS and for Python3

See merge request !62

src/CMakeLists.txt

-if(ADOLC_FOUND AND IPOPT_FOUND AND Python3_FOUND AND dune-uggrid_FOUND)
-  set(programs linear-elasticity)
-
-  # When combining dune-common 2.7 and dune-fufem 2.8, no cmake test for the
-  # Python bindings is ever called (that's not a bug).  In that case
-  # we simply skip building the one executable that needs Python.
-  if(NOT (${dune-common_VERSION} VERSION_LESS_EQUAL "2.7.9" AND ${dune-fufem_VERSION} VERSION_GREATER_EQUAL "2.8.0"))
-    set(programs ${programs} finite-strain-elasticity)
-  endif()
+# Note: PYTHONLIBS_FOUND is only for backwards compatibility with dune-fufem 2.7 and can be removed
+#       in the next release
+if(ADOLC_FOUND AND IPOPT_FOUND AND ( Python3_FOUND OR PYTHONLIBS_FOUND )  AND dune-uggrid_FOUND)
+  set(programs linear-elasticity
+               finite-strain-elasticity)
 
   foreach(_program ${programs})
     add_executable(${_program} ${_program}.cc)