R1:201e0d29435c

Add support for a "containerPHID" in the worker queue

Summary:
Ref T13591. Worker queue tasks which affect commits currently (mostly) store the commit as an "objectPHID", but do not directly reference the repository the commit belongs to.

This can make certain operations (like "change the priority of all tasks affecting repository Y") more difficult than it needs to be.

Support a "containerPHID", similar to the field of the same name on builds, that can store a parent object like a repository and better…