Affiliate URL and promotion method fields

https://github.com/affiliatewp/AffiliateWP/issues/127
https://github.com/affiliatewp/AffiliateWP/issues/225

@pippinsplugins The promotion method is stored in wp_usermeta, how should we show this to the admin for approval? 

Currently it's only sent in registration email, along with website URL. Should we just add this to the standard edit profile screen? The admin would have to remember to go into each affiliate's profile to see the website URL and promotion method before approving. I'm not seeing anywhere else to place them.
`esc_attr` should be `esc_url`. Email body is plain-text, not HTML.