Changes to the docs comments system

Hi!

I've just committed a bunch of changes to how the interactive docs
comment system works. Here's a summary of what has changed:

* Reject and Save for later are now two separate actions. Reject will
*remove* the comment (and notify the author, that's what's different
from delete), Save for later will keep it in the database but *not* show
it on the website.

* Comments are now *hidden* by default, and need to be approved before
they appear on the webpage. To make them easier to check in this case,
there is now a comment preview function.

* The management page (wwwmaster/admin) now lists all unhandled comments
by default without needing to search for anything. The search/filter box
is still there to find specific comments. This also means there is now
an interface available to view all "saved for later" articles for the
person who wants to go through them and incorporate ni the docs.

* A comment can now be in three states: pending, approved,
saved-for-later. Should be self-explaining.

* All previous comments are in a fourth, non-existant state. That means
they will be shown on the website, but they will also appear in th
epending list. That is intentional. Now we just need *everybody* to help
out and go through the old comments and delete/approve/reject them once
again. Note that emails will *not* be sent out for old comments. All new
comments will appear before the old ones. Once all the old ones are
processed, the list will go back down to a nicer size.

//Magnus