add one auth mechenism rather than modify the existing ones

### Try to extend XMPP rather than to modify it

purpose:

add this functions while keeping the old ones work:
* authenticate user with phone number/email
* register with phone number/email

actions:

1. revert the changes to these files:
    * crysasl.erl
    * crysasl_digest.erl
    * crysasl_scram.erl
    * mod_register

2. implement
    * cyrsasl_scram_aft
    * mod_register_aft