Replace has_sidebar config with components
Replace has_sidebar config with components

We had been using a `has_sidebar` field to indicate which of these views
should have a generated sidebar. This replaces that functionality with a
_listing_ of the components that build up the sidebar.

tadhg-ohiggins/regulations-site,tadhg-ohiggins/regulations-site,18F/regulations-site,eregs/regulations-site,18F/regulations-site,eregs/regulations-site,18F/regulations-site,eregs/regulations-site,18F/regulations-site,tadhg-ohiggins/regulations-site,tadhg-ohiggins/regulations-site,eregs/regulations-site