Define available Herald rule repetition options in terms of "isSingleEventAdapter()"

Summary:
Depends on D18924. Ref T13048. Each adapter defines which repetition options ("every time", "only the first time") users may select for rules.

Currently, this is all explicit and hard-coded. However, every adapter really just implements this rule (except for some bugs, see below):

You can pick "only the first time" if this adapter fires more than once on the same object.

Since we already have a isSingleEventAdapter() method which lets us tell if an adapter fires more than once, just write this rule in the base class and delete all the copy/pasting.

This also fixes two bugs because of the copy/pasting: Pholio Mocks and Phriction Documents did not allow you to write "only the first time" rules. There's no reason for this, they just didn't copy/paste enough methods when they were implemented.

This will make a future diff (which introduces an "if the rule did not match last time" policy) cleaner.

Test Plan:

• Checked several different types of rules, saw appropriate options in the dropdown (pre-commit: no options; tasks: first or every).
• Checked mocks and wiki docs, saw that you can now write "only the first time" rules.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13048

Differential Revision: https://secure.phabricator.com/D18925