#1497: Fix bad normalisation on Account.email

[mauromsl]

Closes #1497

• We swap from lowercasing email addresses to using django normalisation function
• Email addresses are normalised at create time, rather than save to avoid modifying existing records
• Usernames are still being lowercased to ensure case insensitive uniqueness at the database level
• Query logic is left untouched, so account retrieval by email for accounts prior to this change should behave as they used to. Lookups by email for new accounts will be case sensitive depending on the DB table collation.

[ajrbyers]

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