Views dynamic entity fields

Think of this situation:

- You have an entity type, with 25 custom fields.
- Your client asks for a report of every entity, plus the values of all the custom fields.

Since rendering every entity is not an option, you have to create a View, and manually add in 25 custom views definitions.

Webform did something similar in #2330557: Replace hard-coded tables with views. But, with some modifications we can do the same for any entity, and any type of field.

So we need
1. A "wildcard" field placeholder, added to every entity type in views, that supports selecting the bundle to use.
2. A hook_views_pre_view() implementation to dynamically add all the fields to the view before it renders.

Using this module
1. Enable "views_all_fields" module
2. Build a view of some type of Entity (content, user, etc.)
3. Add the field "All fields" to your view

When you view that view, all fields on the entity will be dynamically added.