Upgrade Dropwizard version to 0.7.0-rc2

This is related to https://github.com/spinscale/dropwizard-jobs/issues/4 and https://github.com/spinscale/dropwizard-jobs/issues/5 

I've incorporated Hakan's changes and added an extra logic to share the MetricRegistry upon JobBundle initialization:

    SharedMetricRegistries.add("dropwizard-jobs", bootstrap.getMetricRegistry());

Since defaultRegistry() in Metrics is no longer supported. All tests have passed. 

This extension is very useful and I have started to use this at my current workplace. Dropwizard 0.7.0-rc2 is stable enough to warrant a upgrade. I've updated the java version to 1.7 in  the maven build also. Using the latest Reflection 0.9.9-RC1 may not be necessary. Happy to discuss.