Load middleware stacks lazily

This way, the forum middleware does not need to be loaded for
API requests, and vice-versa.

composer.json

@@ -44,6 +44,8 @@
         "league/flysystem": "^1.0.11",
         "league/oauth2-client": "~1.0",
         "matthiasmullie/minify": "^1.3",
+        "middlewares/base-path-router": "^0.2.1",
+        "middlewares/request-handler": "^1.2",
         "monolog/monolog": "^1.16.0",
         "nikic/fast-route": "^0.6",
         "oyejorge/less.php": "^1.7",