Fixed problems in haproxy-marathon-bridge script.

Fixed "unbound local variable" for services which have neither servicePort nor active tasks
Fixed problem with IP-address being used as port in HAproxy for services without a servicePort. Fix skips services where Marathon doesn't return a servicePort
Merge pull request #893 from mikljohansson/master

Fixed problems in haproxy-marathon-bridge script.
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