Allow user customization of the order of accessibility actions and elements in the accessibility descriptions of posts and comments

While RedReader's current order of accessibility actions and post/comment description elements aims to create a reasonable standard, some users might have slightly different preferences (such as opting to hear the subreddit or domain before everything else, etc.), so making the order customizable would improve the UX for these users. Additionally, it should be possible to remove actions/elements.

A few thoughts:

• I think we'll need to create a universal content description for posts/comments, without putting some elements into a title and others into a subtitle. One "accessibility string" containing all elements would allow for complete free user customization.
• To maintain parity with current behaviour, assuming the user has not edited the post/comment description order, enabling concise mode should automatically move "embellishments" before the post title. We shouldn't do this though if the user has customized the order to avoid clobbering user prefs.

The issue names no files, tests, or entry points. Start by locating the existing accessibility descriptions for posts and comments, then define how users can reorder or remove elements while preserving customized preferences and the stated concise-mode behavior.