Add support for filtered lists and batched killing of tasks

Summary:
Adds:
- Filtered listing of apps and tasks
- Batch killing of tasks with configurable size and delay

Test Plan:
Call `list_apps()` with arbitrary filters
Call `kill_tasks` with batch_size and batch_delay

Reviewers: merkkila

Reviewed By: merkkila

Subscribers: tberman, justin, stephan, serdar

Differential Revision: http://phabricator.thefactory.com/D2199