Add metric helper, and metric binding

Changes:

  - Add src/metric.js as an abtraction for monitoring event metrics
  - Add src/bindings/metric.js as another way to add event metrics
  - Update README for metric.js helper
  - Update grunt to copy src/bindings over to dist/bindings
  - Update demo/js/require-config.js with metric helper path
  - Send metric events on load and unload of all views in src/riggr and src/router