* DatePicker: replace native input with el-input

* DatePicker: support size prop, closes #1069, closes #1440

* DatePicker: show correct date for initial value, fixed #1129

* TimePicker: fix empty value when panel appears, fixed #1583

* DatePicker: trigger clickoutside when clicking icon, fixed #1604

* DatePicker: fix year type in year panel, fixed #1607

* DatePicker: fix test

* DatePicker: add doc