Feature: Health checks

@ssorallen Would you take a look at the taskDetailsComponent update?

I updated this page https://github.com/mesosphere/marathon/wiki/Test-App-Commands to contain the toggle server i build to be able to toggle the health of the end point of the health check.
We have been choosing to not render elements if they aren't needed rather than toggle them with hide/show. This shouldn't render if `hideError` is true.