Preserve redirect with /_/ path prefix (#13)

This adds a straightforward way of preserving Farside's redirecting
behavior in the user's browser history. That way if an instance becomes
unavailable between the 5 min scans, the user can opt to navigate back
one page and be taken to a new instance.

This is accomplished using a single line of JS, and could potentially
work as the default behavior of Farside (with the current default
behavior requiring a path prefix instead). This should be revisited down
the road when more people are using this service.

.gitignore

@@ -11,3 +11,5 @@ erl_crash.dump
 
 # Ignore results from update script
 .update-result*
+
+*.rdb