Move libmemcached to nbviewer state

Moving libmemcached to the nbviewer state.

Without it, the first run ends up having installation issues with the Python package for memcache

```
                  _pylibmcmodule.h:42:36: fatal error: libmemcached/memcached.h: No such file or directory
                   #include <libmemcached/memcached.h>
                                                      ^
```