Add Most Popular Cities to Mentors Page

[gcollazo]

• User must be able to see a list of the most popular mentor cities on the mentor's page.
• Each city name must be a link that when clicked will filter the list of mentors
• We must have a permalink for each city

[glortiz]

https://xd.adobe.com/view/b903c847-ee46-44f9-a2e8-1c4eda0d6f33-ec50/screen/ca8cf01b-bedb-4163-8b5a-0dd850562674?hints=on