Implement mutation APIs and prepare for implementing a new UI

ui/tsconfig.json

+{
+  "compilerOptions": {
+    "target": "es5",
+    "lib": [
+      "dom",
+      "dom.iterable",
+      "esnext"
+    ],
+    "allowJs": true,
+    "skipLibCheck": true,
+    "esModuleInterop": true,
+    "allowSyntheticDefaultImports": true,
+    "strict": true,
+    "forceConsistentCasingInFileNames": true,
+    "noFallthroughCasesInSwitch": true,
+    "module": "esnext",
+    "moduleResolution": "node",
+    "resolveJsonModule": true,
+    "isolatedModules": true,
+    "noEmit": true,
+    "jsx": "react-jsx"
+  },
+  "include": [
+    "src"
+  ]
+}

ui/ui.iml

+<?xml version="1.0" encoding="UTF-8"?>
+<module type="WEB_MODULE" version="4">
+  <component name="NewModuleRootManager" inherit-compiler-output="true">
+    <exclude-output />
+    <content url="file://$MODULE_DIR$">
+      <excludeFolder url="file://$MODULE_DIR$/build" />
+    </content>
+    <orderEntry type="sourceFolder" forTests="false" />
+  </component>
+</module>
\ No newline at end of file

util/cors_wrapper.go

+package util
+
+import "net/http"
+
+func CorsWrapper(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Access-Control-Allow-Origin", "*")
+		w.Header().Set("Access-Control-Allow-Headers", "*")
+
+		if r.Method == http.MethodOptions {
+			w.WriteHeader(200)
+			return
+		}
+		next.ServeHTTP(w, r)
+	})
+}

util/method_override.go

-package util
-
-import "net/http"
-
-func MethodOverride(next http.Handler) http.Handler {
-	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		if r.Method == http.MethodPost {
-			method := r.PostFormValue("_method")
-			if method == "" {
-				method = r.Header.Get("X-HTTP-Method-Override")
-			}
-
-			if method == http.MethodPut ||
-				method == http.MethodPatch ||
-				method == http.MethodDelete {
-				r.Method = method
-			}
-		}
-		next.ServeHTTP(w, r)
-	})
-}