Emails should be normalised, as the Postgres database is case sensative

[JonPSmith]

In the current version of AuthP (3.2.0) the email of a user is stored as the user provides it. But an email is NOT case sensitive. This will be a problem as Postgres is case sensative.

The simplest way to do this is add a .Lower to the email in the AuthUser class

Things to do

• Add a .Lower to the email in the AuthUser class (note: do after the username has as been set). DONE
• Apply .Lower to the email in the AuthUsersAdmin FindAuthUserByEmailAsync method. DONE
• Change SyncUsers to normalise Emails. DONE
• Fix all tests containing emails. DONE
• Change each Example to say that "NOTE: The email username is also the password".