Add an activation method to activate webex

Add an activation method to activate webex account when user unable receive external email

Due to company mail policy , 

some users unable to receive external emails.

also we can replace activation mail when customer used SSO+AD+verified domains.

but if they cannot use AD+SSO+verified domains,

they cannot activate account .

so customer need webex add an activation method to activate webex account when user cannot receive external email.