Reconcile health checks after a task is launched

During scale up new tasks are started with a new appVersion. Because each health
check only checks the tasks of exactly one appVersion, the health checks before
the scaling ignore the new tasks.

New health checks are started by the HealthCheckManager on "reconcileWith" which
before this patch was called only after app creation and on leader change. This
patch adds another call after a task is launched and after scale down.

Note, that it would not be enough to call reconcileWith after
MarathonSchedulerActor.scale on scale up because new tasks are launched
asynchronously and reconcileWith would not see new tasks yet.

Fixes #901.
Remove unused imports
Add sbteclipse support to use Eclipse's Scala IDE for development
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

To calculate these two numbers efficiently, the TaskTracker is extended to store the health
value in addition to the MarathonTasks (encapsulated in MarathonTasksWithHealth). The
HealthCheckActor - which receives the health check results from the checks - stores
new health check results in the TaskTracker.
Add app health pie component