Removes active health checks when no longer leader

- Adds HealthCheckManager.removeAll
- Improves HealthCheckManager.removeAllFor
- Normalizes logging in HealthCheckActor
- Fixes #356
Updated MESOS_NATIVE_LIBRARY to MESOS_NATIVE_JAVA_LIBRARY (and retained MESOS_NATIVE_LIBRARY so that Marathon will work for older versions of Mesos)
Remove @author comments. They don't make sense in an open source project.
Cleanup in MarathonScheduler.reconcileTasks
Relocated health check (de)activation call sites
Merge pull request #355 from mesosphere/mesos_native_java_library

Updated MESOS_NATIVE_LIBRARY to MESOS_NATIVE_JAVA_LIBRARY for #352
Merge pull request #357 from mesosphere/issue-356-stop-non-leader-hc

Stop task health checks when no longer leader
Use latest release instead of HEAD for Docker image

Conflicts:
	Dockerfile
Use header for linkability to health check options
Release 0.6.0
Link to 0.6 release in README and update Dockerfile
0.7.0-SNAPSHOT
Update Dockerfile to use the Mesosphere Ubuntu repo
Allow `container` without `executor` in UI

Previously Docker containers had to be run using the Docker executor,
and the UI enforced that by ensuring `executor` was not empty if
`container` was supplied. Now that Mesos supports pluggable
containerization, this is no longer a requirement.
Merge pull request #360 from mesosphere/container-without-executor

Allow `container` without `executor` in UI
Changing FormGroup to be used as an error component
Handling errors in the UI
Review: Indenting
Review: Handling errors in the model
Adding hasSaveError function in model