Pass the just-submitted squelching information to the first AJAX request

If "Add more files" is pressed, the set of selected squelched recipients
is submitted; on the sebsequent page display, however, that information
does not appear in the initial form that is serialized and passed to the
helpers; as such, the state of the checkboxes is lost.

Preserve that information by ensuring that the squelching information is
present on the page during the first page load, before the AJAX
requests, by placing it within the area to be replaced.  This ensures
that the form elements will not be duplicated once the initial AJAX
request returns, but provides the query parameters for the initial call
to jQuery('form[name=TicketUpdate]').serialize().
Remove mostly-duplicate code for Rules which can never trigger

PreviewScrips includes a mostly-duplicated block of code to preview
emails produced by Rules, the mechanism behind Approvals.  However, this
code is unnecessary because /Ticket/Update.html is not accessible for
tickets of type 'approval' (the only objects which could currently
trigger Rules in a stock RT), because /Tickets/autohandler redirects all
but a small number of files under /Tickets/ to /Approvals/ instead.
/Ticket/Update.html is not in the whitelist, and thus cannot render for
Approvals.

Furthermore, the code checks $rule->{hints}{class} to determine if it
should display the rule; no rule ever has a ->{hints} set on it, and
never has, since the introduction of this code in 6d14f535.  As such,
even if /Ticket/Update.html were accessible, or some local customization
made use of Rules for something other than Approvals, they would still
not appear in PreviewScrips.

Remove the duplicated and unused code.
Add squelched recipients as preference

User preference to start with squelch checkboxes unchecked/checked on
ticket reply page. This should respect the semi-permanently squelched
address when applying its logic. If set to true, then the page shows
the checkboxes unchecked - which means the email addresses are *not*
getting any kind of mail.
Additionally, it adds a new config option called $SquelchedRecipients
which allows to set it broadly for all users.
'Select All' checkbox for scrips correspondences/comments

At ticket reply page, we have the option to select/deselect who in the
list of people should receive a copy of the reply/comment. This aims to
add an 'all' checkbox which can select/deselect all of them at once.
Make 'select all' check/uncheck bi-directional

If I uncheck "All $thing", and then I re-check all of the items by hand,
then "All $thing" pops back to being checked as soon as I re-checked
the last item.
Version 0.02 releng