Existing function account_allow() does not seem to be used a whole
lot, and certainly not when approving a registration request.
Created new function send_reg_confirmation_email_from_register
(going for longest-function-name-in-Hubzilla) which attempts to
send such a confirmation email, and also a new email template.
Plugged this into the create_account_from_register function.
Open question: Should the sending of this email be among the success
criteria for the create_account_from_register function?
Since there is no easy way to produce direct links to approve/reject
registrations, create new email template which simply links to the
Accounts admin page.
In response to comments:
- Add type annotations
- Simplify some 'if' statements
- add and fix some whitespace
- simplify input arguments to the function
