The way comments are serialized for use in Review UIs and the diff

viewer is extremely messy. This change is the first step of cleaning

that up.
When I first converted the comment models to TypeScript, I mistakenly

marked the comment editor and comment dialog view's publishedComments

as being BaseComment[]. These are in fact the serialized comment data

arrays. This change moves the definition of the serialized comment

interface out of abstractCommentBlockModel.ts into its own file, where

we can import it anywhere we need, and makes use of that definition

where appropriate.

Ran js-tests.