Accounts with password but no local email can't add an email

[saraolson]

Someone can have a local password and username to log in, but if their email doesn't carry over to local auth after going through the Forgot Password flow, then there's no UI for them to manually add an email in Settings. We should show a text field for these users to add an email address themselves.

Here's a summary of the Settings UI in the various local auth states, the first is what's missing:

1. User has password but no local email:
   We should show a field to add an email address + password confirmation below it. We already show fields to change password.

2. User has local email but no password:
   We show a field to change email address without requiring a password, as well as the fields to add a new password.

3. User has neither local email or password:
   We show the usual 'Add email and password login' fields

4. User has both local email and password:
   We show field to change email address with password confirmation, and fields to change password.

[mayankjx]

Can I work on this issue for hacktoberfest? @saraolson

[saraolson]

@mayankjx we'll be handling this issue internally as we're also redoing the Settings screen UI, but any issue tagged with the Help Wanted label should be open for contributors to take on!