Allow users to "Force accept" package reviews if they own a more general package

Summary:
Ref T12272. If you own a package which owns "/", this allows you to force-accept package reviews for packages which own sub-paths, like "/src/adventure/".

The default UI looks something like this:

[X] Accept as epriestley
[X] Accept as Root Package
[ ] Force accept as Adventure Package

By default, force-accepts are not selected.

(I may do some UI cleanup and/or annotate "because you own X" in the future and/or mark these accepts specially in some way, particularly if this proves confusing along whatever dimension.)

Test Plan:

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12272

Differential Revision: https://secure.phabricator.com/D17569