Feature Request: Allow sponsor account to have unlimited use code.

[kimwhite]

Currently, if seats is set to none 'seats' => " " , a coupon code for unlimited seats is created, however, nothing shows on the Sponsors account page. It can only be seen by admin.

If a cost is not involved and it's just the membership level that can be allowed to be given unlimited uses.

Unlimited messaging appears to be in the code.

https://github.com/strangerstudios/pmpro-sponsored-members/blob/91a2309246628364cdf81d3aa96f9178b60e053d/pmpro-sponsored-members.php#L1916

https://github.com/strangerstudios/pmpro-sponsored-members/blob/91a2309246628364cdf81d3aa96f9178b60e053d/pmpro-sponsored-members.php#L662