initial support for tagging individual data point

to add the tag(s),

POST /rhq-metrics/tags/numeric

{
  "metric": "M1",
  "tags": ["test4", "test5"],
  "timestamp": 11415717856463
}

and to query and filter by tag(s)

GET /rhq-metrics/tags/numeric/test4

or alternatively,

GET /rhq-metrics/metrics/numeric?tags=test4,test5