Upgrades to contact messages (v2)

[joemull]

Replacement PR for #4845 which was merged and then reverted.

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Closes #4138.
Closes #1720.

Notes

• Closes the linked issues
• Connects the contact person and contact message models to account, so that we do not have names and emails outside of the Account object
• Renames the contact person and contact message models to make them easier to read and work with
• Removes stored client IPs to comply with GDPR
• Adds the Django auto-documentation views, which are helpful when searching for template tags and filters, and which show you view and url pairs
• Documents a few things
• Tests for the contact manager and the press and journal contact pages

Screenshots for contact system

Screenshots for admin docs feature

I enabled this in the process of doing this work. It is enormously helpful to view a comprehensive list of things in Janeway sometimes.