adapted cmake to new pdesolver structure

mlmc/src/pdesolver/CMakeLists.txt

 add_library(PDESOLVER STATIC
-        PDESolver.cpp
         PDESolverCreator.cpp
+        EllipticPDESolver.cpp
+        TransportPDESolver.cpp
         assembling/LagrangeEllipticAssemble.cpp
         assembling/MixedEllipticAssemble.cpp
         assembling/HybridEllipticAssemble.cpp