Removing OpauthMemberExtension - it's redundant

Removing file and extension in _config.yml
Log the member in

Removed SetPassword so the user must log in using their social identity.
The SetPassword bit was a bit of a hack anyway. When logged in, the user
is redirected or it falls back to Security.default_login_dest. Working
on the register step now.
OpauthRegisterForm
Docs!