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/calendar/debug.js

@@ -0,0 +1,40 @@
+/*
+ * CalendarFetcher Tester
+ * use this script with `node debug.js` to test the fetcher without the need
+ * of starting the MagicMirror² core. Adjust the values below to your desire.
+ */
+// Load internal alias resolver
+require("../../js/alias-resolver");
+const Log = require("logger");
+
+const CalendarFetcher = require("./calendarfetcher");
+
+const url = "https://calendar.google.com/calendar/ical/pkm1t2uedjbp0uvq1o7oj1jouo%40group.calendar.google.com/private-08ba559f89eec70dd74bbd887d0a3598/basic.ics"; // Standard test URL
+//const url = "https://www.googleapis.com/calendar/v3/calendars/primary/events/"; // URL for Bearer auth (must be configured  in Google OAuth2 first)
+const fetchInterval = 60 * 60 * 1000;
+const maximumEntries = 10;
+const maximumNumberOfDays = 365;
+const user = "magicmirror";
+const pass = "MyStrongPass";
+const auth = {
+	user: user,
+	pass: pass
+};
+
+Log.log("Create fetcher ...");
+
+const fetcher = new CalendarFetcher(url, fetchInterval, [], maximumEntries, maximumNumberOfDays, auth);
+
+fetcher.onReceive(function (fetcher) {
+	Log.log(fetcher.events);
+	process.exit(0);
+});
+
+fetcher.onError(function (fetcher, error) {
+	Log.log("Fetcher error:", error);
+	process.exit(1);
+});
+
+fetcher.startFetch();
+
+Log.log("Create fetcher done! ");