Show current value in configuration list; show default vs non-default values

Summary:
  - When viewing a config list, show the current effective value.
  - Add an icon showing default vs nondefault values.

Test Plan: {F28475}

Reviewers: btrahan, codeblock

Reviewed By: codeblock

CC: aran

Maniphest Tasks: T2255

Differential Revision: https://secure.phabricator.com/D4313