Add exclusion list for metrics from Graphite

You can now configure the `GraphiteReporter` to exclude named metrics by
providing the `excludes` section in the Graphite configuration.

Example:

graphite:
  enabled: true
  prefix: services.example
  excludes:
    - com.example.dao.Person.findPerson
    - com.example.resources.Person.auth.login

The format of the exclusion is: `package.class[.scope].name`. The
`scope` is optional, dependent on whether the metric defines one.