Allowing for using email in addition to username

[xmichaelx]

If user will enter instead of username his email this will check if such email exist and then proceed with authentication.

In order to prevent from guessing username from email whatever user enters will be always returned back to him (thus usage of additional local variable userName).

We can think about adding info that email can be also supplied into localization.

This provides functionality mentioned in #139

[xmichaelx]

Added option for configuring desired behavior for login resolution:

• use username
• user email
• use username or email (if input is a valid email)

In configuration there is additional entry:

"LoginConfiguration": {
  "ResolutionPolicy": "Username"
}

[xmichaelx]

Updated for case where someone has usernames that are valid emails.

[skoruba]

It looks good 👍