Option for user to delete their account/data completely

[alexlittle]

With the new EU General Data Protection Regulations (https://www.eugdpr.org/), we'll soon be required to give users the option to delete their account, and all the data we hold on them.
Should put this option at the end of the edit profile page, but with clear warning that data can;t be recovered, and ask to re-input their password.
Will need to make sure the following is deleted:
user record
user profile record
points
badges
tracker activity
quiz attempts