Add "quotes_allowed" boolean option to $MESSAGE

[Hainish]

Some members do not allow quotes in the message body, viewing it as a potential security risk for the form:

https://github.com/unitedstates/contact-congress/blob/master/members/S000320.yaml

I propose we amend the spec to allow for an additional option for $MESSAGE fields named "quotes_allowed", with a boolean value. We can then use this value in implementations to remove quotes or replace them with something else.

[j-ro]

I'd rather use javascript. There are lots of things that are filtered -- urls (sometimes), quotes (sometimes), it's all a bit fuzzy and tends to change a lot. I think the javascript command would make this easy, if you want to do it that way, and allows us to be more flexible.

[j-ro]

see #1506 for a fix for this in javascript