Story/cite 177: There needs to be an import from Crossref

[PradnyaC11]

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Please provide a brief description of your ticket

The user should be able to search in crossref to references to import. whatever search results from Crossref a user selects should then be imported into citesphere. This could be all search results or just a few or one.

For now, let's put add an entry to the import menu and let the user select which group to import the results into from a dropdown menu.

The importing should be done from Citesphere Importer (not Citesphere), similar how entries from files are imported.

For querying crossref, this library should be used: https://github.com/diging/crossref-connect. However, this is not yet released into maven central, so talk to Julia before picking up this ticket.

... Put ticket description here and add link to ticket ... https://diging.atlassian.net/browse/CITE-177

Are there any other pull requests that this one depends on?

https://github.com/diging/citesphere-importer/pull/22 https://github.com/diging/citesphere-messages/pull/12

Anything else the reviewer needs to know?

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