Added `Publishable` concern

Requires the `published_at` datetime to be present and in the past

Added to:

* `posts`
* `projects`
* `features`
* `visuals`
Fixed inconsistent paging

* Added a `max_per_page` to Kaminari config
* Added a `has_scope :page, default: 1` to `ApplicationController`
Fixed `InheritedResources::Base` pagination

`Paginated` module clobbering `per_page` defaults