Allow line breaks in LegislativeLists

Editors want to have multiple paragraphs in a single LegislativeList entry. In order to allow this, we need to modify the LegislativeList syntax to have an end tag, and treat everything inside it similarly.

Add $EndLegislativeList tag.

After this is released, we need to migrate existing LegislativeLists to the new format. The only place they are being used currently is in Whitehall attachments, so I will open a PR there.