Add DOI to paper
Assign doi to paper on create
Display doi on paper edit
Merge remote-tracking branch 'origin/master' into paper_doi

Conflicts:
	db/schema.rb
schema changed
try assigning doi otherwise nil
reorganize paper factory
Rename doi_start_number to last_doi_issued
mistakenly changed another migration
Merge pull request #629 from Tahi-project/paper_doi

Assign DOI to Papers on Create