The org-ref syntax allows to list multiple citations separated by comma.
This fixes a bug that accepted commas as part of the citation id, so all
citation lists were parsed as one single citation.
Fixes: #7101
Quite a few modules were missing copyright notices.
This commit adds copyright notices everywhere via haddock module
headers. The old license boilerplate comment is redundant with this and has
been removed.
Update copyright years to 2019.
Closes#4592.