Use ApplicationSearch in Ponder

Summary:
Ref T2625. Also modernize some other things:

  - Fix double-"subscribers".
  - Use byline and more standard date.
  - Modernize some of the use of crumbs and navigation.
  - Delete some dead / uncalled code.

Test Plan: {F50669}

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T3578, T2625

Differential Revision: https://secure.phabricator.com/D6486