Improve Altmetric badge support

[alanorth]

OpenRXV currently only checks for Altmetric scores / badges associated with Handles, which causes it to miss some scores. For example, the CGSpace item 10568/118261 has an Altmetric score for its DOI, but not for the Handle itself:

• https://api.altmetric.com/v1/doi/10.1073/pnas.2113947119 → 2211 score (!)
• https://api.altmetric.com/v1/handle/10568/118261 → HTTP 404, no score

When drawing the Altmetric badge in the CGSpace item view we check the DOI first, then the Handle.

[alanorth]

It turns out that the issue, as described, is only a small part of the problem: checking an item's DOI and it's Handle when displaying a badge.

The bigger problem is the API limitations when harvesting handle prefixes. The free API will not let you go past page 100!

• Works: https://api.altmetric.com/v1/citations/at?num_results=100&handle_prefix=10568&page=1
• Works: https://api.altmetric.com/v1/citations/at?num_results=100&handle_prefix=10568&page=2
• ...
• Works: https://api.altmetric.com/v1/citations/at?num_results=100&handle_prefix=10568&page=100
• Doesn't work: https://api.altmetric.com/v1/citations/at?num_results=100&handle_prefix=10568&page=101

We have ~14,000 Handles with attention scores, so we cannot retrieve them all using the free API. We are looking into using the Explorer API with our API key.

[alanorth]

As of #185 we now use the Explorer API with our paid API key and can retrieve all of our handles with attention scores.