Eliom monitoring

resurrect monitoring (fix #99)
one can use the following to monitor a server
```
      <site path="path_to_access_monitoring">
        <eliommodule findlib-package="eliom.server.monitor.start" />
        <eliom />
      </site>
```
- [x] fix hierarchy of information in Eliom section @balat
- [ ] add missing information