* add tabs position

* add tabs test

* Update tabs.md

* TimeSelect: support select with up&down

* using map & indexOf instead of findIndex

* fix select when time disabled

* fix ArrowUp

* TimeSelect: valid data when component blur or enter

* fix: #2514

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