docdrop url mismatch with H api

[perezfr]

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Steps to reproduce

1. to access the docdrop annotations through H web client the url is https://docdrop.org/pdf/HowPeopleLearn_Ch2-34ovo.pdf/
2. To access the docdrop annotations through the H api the url is https://docdrop.org/static/drop-pdf/HowPeopleLearn_Ch2-34ovo.pdf/

Expected behaviour

Tell us what should happen. The two urls should be the same.

Actual behaviour

Tell us what happens instead. There is a mismatch between the url used for the h web client goes and the url for the h api

Browser/system information

Tell us which browser, browser version, and operating system you were using when you encountered this issue.

Additional details

If you have other information which might be helpful, please include it. If a screenshot will help to illustrate the issue you are reporting, please include one.

[dwhly]

@genuineBuildMonkey Any thoughts on how we might fix this?