First version of the monitoring API

Add the routes:
- /entries/<name>/stats
- /entries/<name>/status
- /entries/<name>/start
- /entries/<name>/stop
- /entries/<name>/restart

Please don't merge this pull request right now, it needs to be improved.

I wonder what we should do when someone try to stop an already stopped entry (same thing for the start, stats, …). Right now, I just send "OK". Should I change the response?