Add Europeana (European digital library) as trusted book provider

[Europeana](http://www.europeana.eu/), the European digital library, offers a host of digitized works from European museums. Among others, they include the Gallica collection from the BNF. Europeana's goal seem to be in synch with OpenLibrary's goals.

### Describe the problem that you'd like solved

Add Europeana as a trusted book provider to allow Patrons to access their work.

### Proposal & Constraints

Europeana offers an [API](https://pro.europeana.eu/page/apis), which, as I understand it, is meant for accessing their content from other websites.

Probably not different from other Trusted Book providers.

### Additional context

### Stakeholders