move default modules from /modules/default to /defaultmodules (#4019)

Since the project's inception, I've missed a clear separation between
default and third-party modules.

This increases complexity within the project (exclude `modules`, but not
`modules/default`), but the mixed use is particularly problematic in
Docker setups.

Therefore, with this pull request, I'm moving the default modules to a
different directory.

~~I've chosen `default/modules`, but I'm not bothered about it;
`defaultmodules` or something similar would work just as well.~~

Changed to `defaultmodules`.

Let me know if there's a majority in favor of this change.

defaultmodules/defaultmodules.js

@@ -0,0 +1,10 @@
+/*
+ * Default Modules List
+ * Modules listed below can be loaded without the 'default/' prefix. Omitting the default folder name.
+ */
+const defaultModules = ["alert", "calendar", "clock", "compliments", "helloworld", "newsfeed", "updatenotification", "weather"];
+
+/*************** DO NOT EDIT THE LINE BELOW ***************/
+if (typeof module !== "undefined") {
+	module.exports = defaultModules;
+}