Add "Upvotes" to listings

Many users are asking about adding more UGC/UG actions.

1) Add “Upvote” to the Listing Page header

2) Display the number of upvotes on the listing cards

3) Add sorting by upvotes number to listing grids, apply default sorting as “most upvoted first”

4) Ask anonymous users to sign up/login once they click the “upvote” button. Just open login/signup pages in a new tab for the beginning.