automate wellknown setup

the main reason this is under app and not domain is because it let's
the user know that an app has to be installed for the whole thing to work.

part of #703

src/routes/wellknown.js

@@ -0,0 +1,21 @@
+'use strict';
+
+exports = module.exports = {
+    get
+};
+
+const apps = require('../apps.js'),
+    HttpError = require('connect-lastmile').HttpError;
+
+function get(req, res, next) {
+    const host = req.headers['host'];
+
+    apps.getByFqdn(host, function (error, app) {
+        if (error) return next(new HttpError(404, error.message));
+
+        const location = req.params[0];
+        if (!app.wellKnown || !(location in app.wellKnown)) return next(new HttpError(404, 'No custom well-known config'));
+
+        res.status(200).send(app.wellKnown[location]);
+    });
+}