Implement basic transaction detail blocks

Summary:
Some transactions (like editing configuration values, task descriptions, or Conpherence images) can't be simply explained and need an additional larger element to show them fully (like a text diff).

Support change details like this in ApplicationTransactions. Implements the element in Config, so you can see changes.

Test Plan: {F32974}

Reviewers: chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T2213

Differential Revision: https://secure.phabricator.com/D4984