impl cache create/delete with server create/delete

also impl test connection

app/util/fs.ts

@@ -0,0 +1,19 @@
+import RNFS from 'react-native-fs'
+
+export async function mkdir(path: string): Promise<void> {
+  const exists = await RNFS.exists(path)
+  if (exists) {
+    const isDir = (await RNFS.stat(path)).isDirectory()
+    if (!isDir) {
+      throw new Error(`path exists and is not a directory: ${path}`)
+    } else {
+      return
+    }
+  }
+
+  return await RNFS.mkdir(path)
+}
+
+export async function rmdir(path: string): Promise<void> {
+  return RNFS.unlink(path)
+}