Add image-display toggles on domain and recipe models

[jayaddison]

Describe the reason for these changes and the problem that they solve

Provides support for enabling and disabling recipe and domain icon (favicon) imagery selectively on a per-domain basis.

Briefly summarize the changes

1. Add image_enabled columns to the recipe and domain tables in the database

How have the changes been tested?

1. Database migrations applied, and confirmed that images are not rendered when used in combination with corresponding image-retrieval service code

List any issues that this change relates to
Relates to openculinary/frontend#200.
Relates to openculinary/image-retrieval#8.