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.
Hold off on Font Awesome for right now. That's a lot of overhead to add (82KB) for only 3 or 4 glyphs.