* dropdown 组件 新增触发下拉框显示隐藏时， 触发visible事件，传递当前下拉框显示状态

* Dropdown 修改事件名称，新增文档

* Dropdown 统一事件名称，修改文档

* Dropdown 统一事件名称，修改文档

* 完善form表单prop字段介绍

changed "Datei" (file) to "Daten" (data) and "Einträge" (entries)
completed translation

default-first-option: boolean
* if set to `true`, select first matching option on enter
* only works if `filterable` or `remote` is `true`

test is included

* Update tr-TR.js

update last part

* Update tr-TR.js

table[highlight-current-row] with column[type=expand] will highlight wrong row

For using `done(false)` as well as `vue-router.beforeEach` function `next(false)`.
There are cases when it is necessary.

* Update popup-manager.js

keydown esc, when modal has beforeClose function

* Update popup-manager.js

msgBox.then

* Update popup-manager.js

Fixes issue: https://github.com/ElemeFE/element/issues/4624

* dropdown 组件 新增触发下拉框显示隐藏时， 触发visible事件，传递当前下拉框显示状态

* Dropdown 修改事件名称，新增文档

* Dropdown 统一事件名称，修改文档

* Dropdown 统一事件名称，修改文档

I'm vietnamese developer, so i finished your translate locate! 
Hope you merge my pull request , thanks you ^^