reactor:refine code&&demo

src/components/ThemePicker/index.vue

src/icons/svg/dashboard.svg

src/router/index.js

src/styles/element-ui.scss

src/styles/sidebar.scss

src/vendor/Export2Excel.js

src/vendor/Export2Zip.js

src/views/example/tab/components/tabPane.vue

src/views/example/table/complexTable.vue

src/views/example/table/dragTable.vue

src/views/example/table/dynamicTable/fixedThead.vue

src/views/example/table/dynamicTable/unfixedThead.vue

src/views/example/table/inlineEditTable.vue

src/views/excel/exportExcel.vue

src/views/excel/selectExcel.vue

src/views/layout/components/Levelbar.vue

src/views/svg-icons/index.vue

src/views/zip/index.vue