Carbon

* Table: Fix error in calculate `totalFlexWidth`

* Table: Fix error in caculate `scrollX`

* Table: Watch `max-height` change

* Table: Change `toggleRowExpanded`

* Table: Support `obj[key]`

* Table: Update docs for `toggleRowExpanded`

* Table: Add style and class control for every row and cell

* Table: Add `migrating` mixin for `expand`

* Table: Update test spec

* Table: Add `index` in `table-column` for custom index

# Conflicts:
#	CHANGELOG.en-US.md
#	CHANGELOG.zh-CN.md
#	examples/app.vue
#	examples/index.tpl
#	examples/versions.json
#	package.json
#	packages/dropdown/src/dropdown.vue
#	packages/theme-default/package.json
#	packages/theme-default/src/date-picker/date-picker.css
#	src/index.js

* update custom theme docs

* update form docs

* Table: Trigger `doLayout` when display from `none` to others

* Changelog: update for 1.4.8

* Dropdown: Allow change show/hide timeout by props

* Dropdown: Fixes for document mistake

* fix collapse  bug

* fix code style

* Autocomplete: add value-key

* fix autocomplete test

* Update picker-panel.css

fix "last item been overlapped by footbar bug" when sidebar items are two more。even overflow can not resolve this problem, it is not the same thing. the details you can see https://dulinrain.github.io/elementui/ElementUI%E4%B9%8B%E6%97%B6%E9%97%B4%E6%8F%92%E4%BB%B6Bug.html

* Update date-picker.css

reply to the reviewe of #7567 (https://github.com/ElemeFE/element/pull/7567)

* Update picker-panel.css

remove the previous fix after the review of  #7567(https://github.com/ElemeFE/element/pull/7567)

* Update date-picker.css

* Update picker-panel.css

* Form: add clearValidate

* remove dup attrs