cli support for ActivityRecorder
cli support for ActivityRecorder

Summary:
This adds debug commands for ActivityRecorder:
```
eden debug start_recording --output-dir <DIR>
  * stdout: the id of the profile
eden debug stop_recording --unique <ID>
  * stdout: the output file path
```
Users can record multiple profiles concurrently. Each profile is identified by the timestamp when it started.

Reviewed By: genevievehelsel

Differential Revision: D29666359

fbshipit-source-id: 487ca67de77378a8141bc4ac46b9abd1375ffd23

facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman,nodakai/watchman,nodakai/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman,nodakai/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,nodakai/watchman