Build a web UI to allow addition of Services to a host

• Observer type (start with HTTP-only)
• Friendly name (defaults to URL)
• URL (since we're starting with HTTP-only)
• Ping frequency (e.g. 1 minute)
• Aggregations (e.g. 5 minutes, 1 hour)
• Check response code
• Expected response code (e.g. 200, 100, 404)
• Check RTT (round-trip time)
• Warning RTT
• Failure RTT