Addition model for the call of paper - refactoring twitter metadata - refactoring deadlines matrix in notebook

[eliselavy]

To keep track of the following information

Linked to https://github.com/C2DH/journal-of-digital-history/issues/464

[eliselavy]

@inactinique available in production v1.4.6 / v3.4.1 Need to discuss at a future meeting how can improve this as for the moment:

• addition of the dates in a dedicated notebook
• addition of the dates in the metadatas for twitter
• addition of the dates in the call of paper model in the admin site

Sent reminder automatically ? Provide view if authors are late? ...