Mask remaining config values, and implement `set` type

Summary: The remaining hash/key values are already-migrated, I am just bad at grep. Also implement a "set" type.

Test Plan: Looked at set, edited set.

Reviewers: codeblock, btrahan

Reviewed By: codeblock

CC: aran

Maniphest Tasks: T2255

Differential Revision: https://secure.phabricator.com/D4476