Add link to contribution from Abstract View (Accepted)

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# Ticket imported from Trac
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[RQF0211491]

When an abstract is accepted we should see a link, in the AbstractDisplay.py page, to the associated contribution.

Start by opening AbstractDisplay.py and tracing how an accepted abstract is rendered and how its associated contribution is identified. Add the contribution link in the accepted-abstract view, with completion indicated by the link appearing for accepted abstracts and remaining absent when no contribution is associated.

Written by the indexing model from the issue text.