Add tagging support

[jotak]

• Provide global tags (all metrics)
  builder.addGlobalTag("myglobaltag", "value")
• Provide predefined per-metric tagging
  builder.addTag("mymetric", "mytag", "value")
• Provide automatic tagging on Meters (and Timers when it's done)
  tag=timer:1min, tag=timer:5min, tag=timer:count etc.

Note that Hawkular Metrics doesn't allow "on the fly" tagging when metrics are pushed. So we must implement a mechanism to check if tags are already defined, tag them if they're not, cache them with an eviction system, without using high level library such as guava since we don't want add dependencies.