Bugfix: a reference cited with new text locked the database

• cite() found an existing citation only by its raw text. SEAMM's own citation
  holds its version in the text, so after an update it was inserted again and
  failed on the unique alias/DOI ("UNIQUE constraint failed: citation.doi"),
  leaving the transaction open. That held the database's lock: a resumed SEAMM job's
  parallel iterations then all failed with "database is locked" (SEAMM job 5366).
• Citations are now also found by alias or DOI, with their text brought up to
  date; a failed citation is rolled back; and connections wait up to 30 s for a
  lock, since the iterations of a parallel loop share the job's database.