[Improvement] Picker: rewrite (#370)

* [Improvement] Picker code review

* fix: Picker text cases

* fix: Picker watch defaultIndex

* [Improvement] Picker support simple data struct

* [bugfix] Picker defaultIndex out of range

packages/utils/deep-clone.js

@@ -0,0 +1,10 @@
+import deepAssign from './deep-assign';
+
+export default function deepClone(obj) {
+  if (Array.isArray(obj)) {
+    return obj.map(item => deepClone(item));
+  } else if (typeof obj === 'object') {
+    return deepAssign({}, obj);
+  }
+  return obj;
+}