Checkpoint commit
Thanks to exor674 for looking at this and telling me what I was missing!
This commit establishes the last of the basic functionality, and it's
working: closing and reopening comments, printing "Comments closed" when
comments are closed, and removing the reply link on individual comments
when comments are closed.

Next steps:
* split close-comments into its own item in the Comments pane of update page
* establish an 'allow replies only, not top-level comments' option
* add a 'close comments after $time' option on creating entry
* (and make it so that it actually, you know, closes the comments on time)
* add an account-wide preference for closing comments on all entries on timed basis
* add the appropriate text properties into non-TR base layouts