Add a view to add watchers
Refactor AddWatcherView
Fix unit tests
Refactor add and
Update signal handlers to use decision
Add url for AddWatcher view
Add url for remove watcher view
Fix bugs in watcher view
Fix observation adding and removal
Add checkbox to watch/unwatch item to the view
Add References: email header for better threading

particularly for comments.

The References: header has a list of all message-id:s of messages that
have come before it, so it allows threading even if the last message
wasn't received by you (as it wouldn't be if you entered it yourself on
the site).

Before this, if you enter a feedback on the site, then comments to the
feedback won't find the message-id referenced in the In-Reply-To:
header, so the comment email will start a new thread.
Merge pull request #202 from foobacca/references_header

Add References: email header for better threading

Merging my own pull request after talking to TomL
Add 'watch' field to comment form to allow users to say if they wish to
observe an item
Change discussion to read conversation

Discussion is an econsensus reserved word. Using it in text could be
confusing, so I'm using conversation instead.
Update labels on watch fields and make them true by default
Remove hardcoded strings

Replace all instances of "decision_change" with a constant
Add watcher hadniling to forms
Add signal handling code for notification settings
Merge branch 'notification_settings' into develop

Conflicts:
	django/econsensus/publicweb/models.py
Merge branch 'develop_main' into develop

Conflicts:
	django/econsensus/publicweb/models.py