Refinements and alerts

[anjackson]

This change set:

• Adds alerts for many critical cases, like CDX lag.
• Fixes Stats Pusher submits multiple metrics #21 for stats pusher.
• Add RR log count to stats pusher.
• Tidied the alerts up into two groups.
• Added wa-www mtail, and HDFS web endpoints to the monitoring configuration.

[anjackson]

BTW, once deployed, the Reading Room Logs alert will fire, because we don't have NLW and NLS logs (i.e. we have 8 not 10 recently-updated log files). So you'll need to silence it for a bit.