Use Javelin placeholders and new sorting rules broadly; consolidate tokenizer construction code

Summary:

• We have three nearly-identical blocks of Tokenizer construction code; consolidate them into Prefab.
• Add placeholder support.
• Augment server-side stuff to specify placeholder text.

Test Plan: Verified behavior of Differential edit tokenizers, Differential comment tokenizers, Maniphest edit tokenizers, Maniphest comment tokenizers, Maniphest filter tokenizers, Differential filter tokenizers, Owners filter tokenizers, Owners edit tokenizers, Herald edit tokenizers, Audit filter tokenizers.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran, epriestley

Maniphest Tasks: T772, T946

Differential Revision: https://secure.phabricator.com/D1844