Allow italics in a variety of content fields

[joemull]

This branch adds support for italics in a variety of content fields, especially those that might include journal titles or other titles of works that need italicization.

We can do this more easily and safely now thanks to safer storage of HTML in the database introduced in 1.5.1.

For the copyright text, I have opted to avoid putting the journal name altogether. This will require a retranslation of that string but I believe it is worth it because the existing translation is not ideal, because it's a partial sentence (excludes the journal name) and does not include punctuation as part of the translated string (the colon).

[joemull]

Oh. Not quite ready. Problem with migrations.

[joemull]

@ajrbyers I just wanted to make sure you saw this one is ready for review now.

[joemull]

I've just given this a once over and before I test it out I wondered if there was a reason why the Frozen Author records had all been convered to bleach fields?

Ah, yes it's because they get used in the carousel subtitle. We said we wanted to support italics in carousel text.

[ajrbyers]

@joemull just FYI this PR now has a conflict.

[joemull]

@ajrbyers After rebasing I ran tests and picked up several things that needed to be addressed:

1. Utilities like importers trying to save None to affected fields on FrozenAuthor and IssueType
2. Fields from the Account model that allow null=True being directly saved to FrozenAuthor

I think this calls for standardizing the corresponding Account model fields, so I've done that. What do you think? Re-requesting review since it's a significant enough change.

[ajrbyers]

@mauromsl assigning this to you for a second review as the changes are significant.

[joemull]

Rebased to resolve conflict in migration_utils.