Reorganize project. Add folder for shared code between backend/dashboard. Switch from jest to ava for tests.

backend/src/SimpleError.ts

@@ -0,0 +1,13 @@
+import util from "util";
+
+export class SimpleError {
+  public message: string;
+
+  constructor(message: string) {
+    this.message = message;
+  }
+
+  [util.inspect.custom](depth, options) {
+    return `Error: ${this.message}`;
+  }
+}