Fix and uniform the usage of Graph and Parent typedefs (#268)

- Rename Graph typedefs to GraphType in the implementation of graph
maps and MapExtender to prevent conflicts (especially using VS).
They are not public.
- Make Parent typedefs private in all classes.
- Replace Digraph with Graph in some places
(fix faulty renamings of the script).
- Use Graph and Digraph typedefs (more) consequently.

 INCLUDE_DIRECTORIES(

   ${PROJECT_SOURCE_DIR}

   ${PROJECT_BINARY_DIR}

 )

 LINK_DIRECTORIES(${PROJECT_BINARY_DIR}/lemon)

 SET(DEMOS

   arg_parser_demo

   graph_to_eps_demo

   lgf_demo)

 FOREACH(DEMO_NAME ${DEMOS})

   ADD_EXECUTABLE(${DEMO_NAME} ${DEMO_NAME}.cc)

   TARGET_LINK_LIBRARIES(${DEMO_NAME} lemon)

 ENDFOREACH(DEMO_NAME)