Flags yellow for annotations that match case insensitive error

[codefromthecrypt]

Particularly, this flags existing finagle formatted errors, like so:
"Server Send Error: TimeoutException: socket timed out"

Fixes #1472
See openzipkin/openzipkin.github.io#52

[codefromthecrypt]

Using this data:

curl -H "Content-Type: application/json" -s localhost:9411/api/v1/spans -d '[
  {
    "traceId": "4e441824ec2b6a44",
    "id": "4e441824ec2b6a44",
    "name": "get",
    "timestamp": 1478624611519000,
    "annotations": [
    {
      "timestamp": 1478624611519000,
      "value": "Server Send Error: TimeoutException: socket timed out",
      "endpoint": {
        "serviceName": "zipkin-server",
        "ipv4": "192.168.99.1",
        "port": 9411
      }
    },
    {
      "timestamp": 1478624611519001,
      "value": "{\"foo\": \"bar\"}",
      "endpoint": {
        "serviceName": "zipkin-server",
        "ipv4": "192.168.99.1",
        "port": 9411
      }
    }],
    "binaryAnnotations": [
    {
      "key": "bar",
      "value": "bar",
      "endpoint": {
        "serviceName": "zipkin-server",
        "ipv4": "192.168.99.1",
        "port": 9411
      }
    },
      {
        "key": "foo",
        "value": "{\"foo\": \"bar\"}",
        "endpoint": {
          "serviceName": "zipkin-server",
          "ipv4": "192.168.99.1",
          "port": 9411
        }
      }
    ]
  }
  ]'

[codefromthecrypt]

@kevinoliver @mosesn better late than never :P

[codefromthecrypt]

(ps ignore the escaped json in the spans.. that's unrelated)