Fix links to datasets when the URL to the project ends in a slash

Addresses #1680

This fixes that.  Long story short, Rails routes /projects/1 and /projects/1/ the exact same way.  However, relative paths in browsers work differently - a relative path without a forward slash inserts itself after the last forward slash, while a relative path with a forward slash inserts itself after the first one.  The links previously did the former, now they do the latter.