stream links: Use more standard API to go to location.

For stream links inside messages (like "#social") we
now use these functions:

    hashchange.go_to_location:

        We don't need to set href.  Relative paths
        are more standard, and the url is already
        encoded.

    hash_util.by_stream_uri:

        This saves a step in building the URL.

static/js/click_handlers.js

@@ -197,7 +197,7 @@ exports.initialize = function () {
         // so we re-encode the hash.
         var stream = stream_data.get_sub_by_id($(this).attr('data-stream-id'));
         if (stream) {
-            window.location.href = '/#narrow/stream/' + hash_util.encode_stream_name(stream.name);
+            hashchange.go_to_location(hash_util.by_stream_uri(stream.name));
             return;
         }
         window.location.href = $(this).attr('href');