CE-1103 Show a notification if a given wikia is available in the user's native language

https://wikia-inc.atlassian.net/browse/CE-1103

This is an extension that shows a notification if a wikia visited by a user has a sibling wikia in the user's native language. The check for the target language is based on a value of the *Geo* cookie. Then, there is a request sent via Nirvana to check if there is a record in the *city_list* table with a value of *city_url* matching the converted url (e.g. *http://community.wikia.com* is converted to *http://ja.community.wikia.com).

Currently, the only language that is supported is Japanese. However, adding a new language is a piece of cake and takes only adding an entry to an array in the JS module.

CC: @Grunny, @macbre, @nandy-andy 
To make the full use of HTTP caching GET request should made (instead of POST, which is the default for nirvana and by the definition is used to modify the state on the server).