Voting feature

When a product is "coming soon", a voting form is added under the label, allowing visitors to vote for the products they want the most.

The admins can then see in the dashboard which products are most wanted and prioritize the development of new products. A count of the votes is also available on each product page, right under the "Coming soon" checkbox.
I tried to hook earlier as there is a `wp_redirect()`at the end of `edd_coming_soon_increment_votes()` but I'm not against using `template_redirect` instead if you feel it's more appropriate.