White Labeled license key shows all the license keys of the owner

[bfintal]

1. Use an owner that has multiple license keys
2. Activate one license key (not white labeled) on a website
3. Enable white label on that license key
4. Sync the license key in the website, it's now white labeled
5. Try changing the license key in the website, it will show all the license keys of the owner

If white labeled, the license keys should not be visible

[fajardoleo]

@bfintal This is already in progress (will be part of this PR: https://github.com/Freemius/wordpress-sdk/pull/650). Thanks!