Change handling of external IDs in search UI

[mariagould]

Per ror-community/ror-api#173 we wish to format external IDs as URLs in the ROR API. This means that ror-app should take the URL form from the API instead of transforming external ID strings into URLs.

Still to be determined: How should the external IDs be displayed in the search UI?

Currently, they are displayed as strings but formatted as actionable links, e.g., an ISNI written as 0000000121736488 that resolves to http://isni.org/isni/0000000121736488. Should this remain the case or do the full URLs need to be exposed?