Add BaseURL configuration (fixes #103)

ui/src/utils/baseUrl.js

@@ -0,0 +1,8 @@
+const baseUrl = (path) => {
+  const base = localStorage.getItem('baseURL') || ''
+  const parts = [base]
+  parts.push(path.replace(/^\//, ''))
+  return parts.join('/')
+}
+
+export default baseUrl