Remove metrics-scala.
Totally revamp metrics-core.

Big new changes:

* Meter and timers no longer have units. Units will be the responsibility of reporters.
* Metrics are identified by dotted names, not quasi-ObjectNames.
* Reporting architecture has been radically simplified.
* You can register metrics not created by the registry.
* Separated health checks into their own modules.
* No more default registries.

I've pinned the other modules to metrics-core 2.2.0 to make a progressive upgrade easier.
Added metrics-healthchecks.
Bump the various modules back to 2.2 API.
Add metrics-jvm.

Not at all ready for prime time yet.
Added builders for metric names.
Move metrics-web to 3.0.
Bring annotations around.
Revamp metrics-jersey.
Revamp metrics-httpclient.
Upgrade some dependencies.
Stop grouping metrics by type in JMX.
Revamp metrics-ehcache.
Don't unnecessarily convert longs to doubles.
Added LoggerReporter.
Added getNames to HealthCheckRegistry and MetricRegistry.
Added runHealthCheck to HealthCheckRegistry.
Remove all the clear methods.
Revamp GangliaReporter.
Fix counter names in GangliaReporter.