consistent headernav

[dalekunce]

@danbjoseph @giblet22 can you go through the site and make sure all the nav headers are consistent.

@danbjoseph can you do a little research to see if we can maintain the header and css somewhere centrally so we don't have to keep repeating it in all the sub repos.

[danbjoseph]

• the nav header is included on all pages, so should be consistent
• the leaderboard and user pages end up dropping the language picker but that is a separate issue discover tab in different languages #275
• all the custom styling should be in app/assets/styles/*.scss and compiled into a single file that is loaded as part of the default layout

[dalekunce]

closed via #530