Improved data tables layout

Basically set all outline options to "none", and exposed the following css classes to facilitate their customization:

.vue-ui-data-table
.vue-ui-data-table__caption
.vue-ui-data-table__thead-row
.vue-ui-data-table__tbody__row
.vue-ui-data-table__tbody__row-even
.vue-ui-data-table__tbody__row-odd
.vue-ui-data-table__tbody__td