move mpi library code into library

miniapp/CMakeLists.txt

 set(HEADERS
 )
 set(MINIAPP_SOURCES
-    mpi.cpp
+    #    mpi.cpp
     io.cpp
     miniapp.cpp
 )

src/CMakeLists.txt

@@ -7,6 +7,9 @@ set(BASE_SOURCES
     parameter_list.cpp
     swcio.cpp
 )
+if(${WITH_MPI})
+    set(BASE_SOURCES ${BASE_SOURCES} communication/mpi.cpp)
+endif()
 
 add_library(cellalgo ${BASE_SOURCES} ${HEADERS})
 add_dependencies(cellalgo build_all_mods)