Add app health display in application list of web UI

This commits add a health summary in the application list component of the weg UI.
To do this two new attributes are added to the /v2/apps JSON:

  tasksHealthy, tasksUnhealthy

These numbers are calculated in the MarathonHealthCheckManager by counting the
aggregated health check results of all tasks of an app.
Add app health pie component
Show over-capacity tasks in blue in health pie chart
Display health pie chart for suspended apps correctly in black