Summary: Although I don't want to end up with 20 of these again, this is a reasonable default to provide, particularly for installs where a large portion of the userbase primarily reports bugs and does not interact with them directly.
Test Plan: Hit `/maniphest/`, saw "Subscribed", clicked it, saw the tasks I'm subscribed to.
Reviewers: jbrown, btrahan
Reviewed By: jbrown
CC: aran
Maniphest Tasks: T4100
Differential Revision: https://secure.phabricator.com/D7586
965c2e6732