BUG/FEAT: Add affiliation author label

[htwangtw]

I found some inconsistent behaviour of corref in PDF and webpage rendering.

Current behaviour:
AFAIK the corref in the template comments indicates it's a way of showing the primary affiliation of authors with multiple affiliations on the web. It is compulsory otherwise the web page won't build correctly.
In the PDF built this tag is not really used for the same thing it seems -
corref seems to link to correspondence author's affiliation, but there's no way to indicate correspondence author.
The PDF template just take the last author with corref tag as the correspondence author.

Expected behaviour:
corref indicates the primary affiliation of the correspondence author.

Desired behaviour:
corref indicates the correspondence author.
Add primaff to indicate the primary affiliation of any authors with multiple affiliations.