Allow upload via PMC ID

[Daniel-Mietchen]

Some articles in PMC do not have DOIs, and a (small) subset thereof is openly licensed (e.g. http://www.ncbi.nlm.nih.gov/pmc/journals/896/ ), so it would be good if the web form would also accept PMC IDs.

[notconfusing]

this shouldn't be too difticult because the first thing we do is convert the DOI to PMC ID