Generic host monitoring (Agentless)

[Zeniic]

Firstly, love the project! Already started using this as an alternative to my Zabbix environment (Admittedly it's overkill and I wanted something lightweight with less admin overhead).

---

On to my feature suggestion:

The agent based monitoring is fantastic but in some cases it may be useful to monitor services I do not administer (For example, a Public service or Shared Web Hosting where access to the command line is limited or impossible).

Of course, an agentless monitor can't pull metrics but in some cases even a simple ICMP / Ping can provide a nice level of visibility / notifications.

[henrygd]

Maybe I can add simple ping or 200 status monitors, but probably not in the very near future.

It might also be nice to add the functionality to the agent so you can ping LAN devices, as suggested by @pickles4evaaaa in #91.