[PATCHES] pgarchives: merge schema.sql into Django's model

As discussed in previous threads before [1, 2], database creations file are currently split between the Django model and a SQL file. Discrepancy in the database's definition exists between them. As a consequence, the database cannot be created easily.
This series of patches merge schema.sql into Django's model, and adds specific postgres components that cannot be handled by Django's ORM using RunSQL() in a migration file.

Please also note that I integrated several other patches to avoid multiple migration files:
- I allowed message.parentid to be null, as discussed in [1]. This can cause Internal Server Errors in views.py, which are fixed by the second patch.
- I used BinaryFields for bytea columns (message.rawtxt and attachments.attachment), which seems to be the way to integrate bytea into Django

It may be a good opportunity to remove all mentions of pg_dict, pg_stop and associated file. I'm not sure of the consequences of this. According to [2], these are the remains of an aborted idea.
Also, what does tsparer bring? Can the installation of pgarchives be simplified by replacing it with pg_catalog.english?

[1]: https://www.postgresql.org/message-id/CABUevEyFpYPEHh0AAyTAsgymRKOOVA1SY_pDHPCbBQQ9BawfTA%40mail.gmail.com
[2]: https://www.postgresql.org/message-id/CABUevEy_i1xAKscMv4KZ0%3DbE8050bBcQfWaNyjwZZBofZx7JgQ%40mail.gmail.com
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Célestin Matte