We need to add an ORDER BY clause; not doing so was causing different
processes to show up sometimes. As mentioned in the PostgreSQL manual:
> Because the order of the rows in the database table is unpredictable,
> when you use the LIMIT clause, you should always use the ORDER BY
> clause to control the order of rows. If you don’t do so, you will get
> an unpredictable result set.
The condition `params[:page_id] != 0` didn't work properly when editing
the homepage because in that case the parameter was `nil`, and the line
`SiteCustomization::Page.find(@card.site_customization_page_id)` raised
an exception because it couldn't find a page with a `nil` ID.
Fixing the issue while maintaining the check against `0` lead to complex
code, and so allowing `nil` in the database and assuming cards with no
`site_customization_page_id` belonged in the homepage seemed to be the
easiest solution.
Note there is some funkiness going on with class loadings
Had to create a `feed` and `widget_feed` table even though in this
first version the Widget::Feed includes only uses ActiveModel instead
of ActiveRecord, otherwise some specs failed
We’ll figure it out and clean up 😌
