Allow SE-ARC to target different inputs on the site

This change set enables SE-AutoReviewComments to supply default strings for the edit summary and custom off-topic reasons when closing a question.

The change introduces new prefixes that can be applied to comments, to mark them as only being applicable to a certain type of target.

Previously, only Q (question) and A (answer) was available. The new prefixes are:

- C = Closure
- EA = Edit summary for Answers
- EQ = Edit summary for Questions