Using Email for Demo without TOTP

[Cabalist]

I am getting a crash when trying to use the otp_email by itself.

It appears the code calls allauth_2fa.utils.user_has_valid_totp_device() without checking to see which device(s) are installed. Since in our demo app we just have 'django_otp.plugins.otp_email', and none of the others devices installed we get the following error relation "django_otp_totpdevice" does not exist

Adding 'django_otp.plugins.otp_totp', to the INSTALLED_APP fixes this issue but then pushes the user through the TOTP flow instead of using email.

Given that there are other devices in the django_otp ecosystem (HOTP, Static, etc) it might be worthwhile to have user_has_valid_totp_device() replaced by something more generic user_has_valid_device with some logic to detect the install apps.

[clokep]

This seems related to #23. The current code has some assumptions that TOTP wants to be enabled. If you can figure out a good way to generalize this, I'd be happy to include any changes!