Reduce code duplication in Herald fields

Summary:
Ref T8726. I want to modularize values and reduce how hard-coded / copypasta'd they are.

• Rename get...StandardCondition() to get...StandardType(), since we can drive both conditions and values from it.
• Rename STANDARD_LIST to STANDARD_PHID_LIST for consistency: all "lists" are lists of PHIDs.
• For all standard types which don't require typehaeads, lift their logic into the base class.
• I'll lift typeaheads soon, but need to generalize them first.

Test Plan: Edited various Herald rules, saw value UI generate correctly.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T8726

Differential Revision: https://secure.phabricator.com/D13612