refactor: extract application construction and lifecycle

scripts/package-boundaries.json

@@ -10,6 +10,28 @@
       "src/data/localGeojsonCore.js",
       "src/data/localGeojsonLod.js"
     ],
-    "external": ["cesium"]
+    "external": [
+      "cesium"
+    ]
+  },
+  "application": {
+    "exports": [
+      "./application"
+    ],
+    "modules": [
+      "src/app/application.js"
+    ],
+    "external": []
+  },
+  "viewer": {
+    "exports": [
+      "./application/viewer"
+    ],
+    "modules": [
+      "src/app/viewer.js"
+    ],
+    "external": [
+      "cesium"
+    ]
   }
 }