Added manager to module when casting so importable via migrations, re…

[jamesoutterside]

Added manager to module when casting so importable via migrations, removes need for deconstruct.

• Addresses issue extra migrations for user model - keeps on adding migrations with manager #6
• When managers (like UserManager) set use_in_migrations, deconstruct returned original manager, leading to incorrect then repeated migration.
• Made Privacy{}Manager part or module so deconstruct is not needed and can be called as a normal manager in migrations.

[coveralls]

Pull Request Test Coverage Report for Build 41

• 10 of 10 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 39:	0.0%
Covered Lines:	523
Relevant Lines:	523

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💛 - Coveralls