Widget needed for email or phone number

[jace]

Funnel needs a mixed-use widget in two places:

1. The login form currently accepts "username or email"
2. The registration form currently accepts an email address

There is a pending requirement to add support for a phone number (in funnel/issues#693), turning these use cases into:

1. Login: Username or email address or phone number
2. Register: Email address or phone number

A backend validator can detect the content type and process accordingly. The front-end however needs to give the user a hint of what is going on, and the UI pattern adopted by Decathlon may be our best inspiration.

The front-end widget must switch widget type and appearance based on which of the following regex patterns match:

1. International phone: \+[0-9. -]+ (allows period, space and dash in input, to be stripped later)
2. Local phone: [0-9. -]+
3. Email: .*@.*
4. Default: input type="text" (assume username)

The difference between international phone and local phone is that a guessed country code must appear when in local phone mode, as the submitted field will need to include the +country prefix. The code can be guessed from IP address location or browser timezone, using libphonenumber. (The server can send this pre-filled in the form to avoid adding a new JS library.)