[Literature] Automatic citation count retrieval

[RianneAr]

In update_bibfile.py, the function get_citations does not work always properly. It loops over all citations, taking a very long time. Up until now, this function has been replaced by:
def get_citations(semantic_scholar_ids, sch):
dict_cits = {}
ss_ids_not_found = []
for ss_id in semantic_scholar_ids:
break
return dict_cits, ss_ids_not_found

When the literature update was run.

[michellestegem]

Sometimes semantic scholar gives citation counts that are much smaller than the existing stored ones. This should be investigated to determine why it happens and if anything can be done to fix it. Currently the code prints a warning if (previous_cits > (1.5 * n_cits)) and (previous_cits - n_cits > 10) ... these are the cases of interest.
On a related note, doi.org returns citations which are stored in the field "citation-count" - should investigate if these are accurate, although at one time I think we decided they were not. (Could check what doi.org gives for the cases of interest mentioned above, for example)