Fix modals dependency cycle.

This commit forces the files that create modals to create their own
modal closing function instead of creating all of them in the modals
file. These functions are then passed to the modals.close object. This
is intended to remove modals.js's dependencies on these other files.

static/js/drafts.js

@@ -376,6 +376,12 @@ exports.launch = function () {
 };
 
 $(function () {
+
+    function drafts_close_modal() {
+        hashchange.exit_modal();
+    }
+    modals.set_close_handler("drafts", drafts_close_modal);
+
     window.addEventListener("beforeunload", function () {
         exports.update_draft();
     });