cron harakiri and stats

I've ended up adding uwsgi_cron->harakiri since I think we will need per command harakiri timeout. Commands might be different and they might require different harakiri settings, with this patch we have global --cron-harakiri setting, but we should also add possibility to set this per cron task, this patch allows it, we just need to pick up syntax.

Would this be ok?
```
cron2 = minute=-2,week=1,harakiri=30,unique=1,legion=mylegion my fancy command
```
We could use "-1" as default value for crontab fields so user would only need to set few of them in most cases.
Everything after the key=val list would be interpreted as the command to run.