fix all picker's transition and styles, including select, autocomplete, timer-picker, date-picker
and so on, which transition should be 'el-zoom-in-top' and without duplication.
* feat(checkbox): init checkbox
* feat(checkbox): update checkbox-button checkbox-group
* feat(checkbox): init unit test
* feat(checkbox): update unit test
* fix(checkbox): improve some code
* test(checkbox): update test case