More fixes that make autotools working for the empty repo

- Add a dummy lemon/list_graph.h file and put it in the Makefile.am
- Remove the unnecesary icons from doc/icons/geom folder.
- Update .hgignore

 EXTRA_DIST += \

         benchmark/Makefile

 if WANT_BENCHMARK

 noinst_HEADERS +=

 noinst_PROGRAMS +=

 endif WANT_BENCHMARK