Add alarming states to Metric graphs

Graphs will change colour based on the current warning state using traffic lights colours; green is normal, orange is warning, red is error. Negative alarming is possible to warn when metric values go below thresholds.
With auto-refresh on the Metric show page the graph will change colour on update if necessary. 

Since Graphite can be a strange beast and provide a null or 0 for the last datapoint we use the second-to-last datapoint for detecting Graphite metric alarm states. Cloudwatch has no such issue.