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