Only emit change for user input

Before:
  select.value = 1;   // triggers change

After:
  select.value = 1;   // does not trigger change

When <el-form> missing `model`, validate will return false, then throw a warning to facilitate the developer troubleshooting

* Tree: add current node method

* Tree: remove current-node-key attribute

* fix warn message

* Update tree.md

* Update tree.md

* Tree: update doc

* fix doc

未改之前，设置禁用日期后，年和月的禁用状态不准。因为只选取了年和月的某一天进行判断。修改为年和月的每一天都进行判断。

* DatePicker: Fix Typing a date and tabbing does not close the calendar #4948

* DatePicker: Fix Typing a date and tabbing does not close the calendar #4948 -Updated test case

* Fixes #4931

* feature menu collapse

* Update menu.md