Contributions page user not found message - bad link on page

[bgirardot]

If you try and search for a user that does not exist, the resulting error message has a link that is bad, the Contribute button links to a url that does not exist. For example

http://www.missingmaps.org/users/#/notarealuser

[mojodna]

The "contribute" link in the header also goes to a page that doesn't exist (http://www.missingmaps.org/contribute/).

[danbjoseph]

needs to be /learn/ or /validate/ (nav headers on the user profiles and leaderboard pages are built differently from the rest of the site and weren't updated when the /contribute/ page was changed)

[dalekunce]

I fixed the 404 link error with #384
@mojodna was looking into the case issues