Auto-update TaskListComponent

This is the same code as from the AppListComponent, only with a
significantly shorter polling interval.

Conflicts:
	src/main/resources/assets/js/dist/main.js
	src/main/resources/assets/js/dist/main.js.gz
Merge pull request #283 from Shopify/auto-update-task-list

Auto-update TaskListComponent
Show running tasks in app list
Merge pull request #284 from Shopify/show-running-tasks-in-app-list

Show running tasks in app list
Added abdication of leadership on disconnect from the Mesos master. Also reworked the MarathonSchedulerService class to properly handle leadership defeats/elections.