refactor: Extract reload_state module.

This is part of work to break some of our
nastier circular dependencies in preparation
for our es6 migration.

This commit should facilitate loading leaf-like
modules such as people.js before all of the things
that reload.js depends on.

frontend_tests/node_tests/presence.js

@@ -5,7 +5,7 @@ var return_false = function () { return false; };
 
 set_global('server_events', {});
 set_global('blueslip', {});
-set_global('reload', {
+set_global('reload_state', {
     is_in_progress: return_false,
 });