It's very easy to forget to add `require 'rails_helper'` at the top of every core/plugin spec file, and omissions can cause some very confusing/sporadic errors.
By setting this flag in `.rspec`, we can remove the need for `require 'rails_helper'` entirely.
When the linked topic is created we'll not hardcode the topic title and
let onebox work its magic instead so that the title can be updated
automatically.
This commit adds a site setting `auto_close_topics_create_linked_topic`
which when enabled works in conjunction with `auto_close_topics_post_count`
setting and creates a new linked topic for the topic just closed.
The auto-created new topic contains a link for all the previous topics
and the topic titles are appended with `(Part {n})`.
The setting is enabled by default.
