Adding a mask to the CEP (zipcode)

Hi, this pull request adds a mask to the CEP field of the Correio Simulator. It was necessary to incorporate the mask jquery plugin, which wasn't available anywhere else. I used the wp_enqueue_script as already used for the other JS. Wasn't totally sure if the JS event would be the best one to apply the mask, please feel free to change it or let me know if you want me to use another JS event..