added checkbox - work with or without button group
added checkbox - work with or without button group

yuche/vue-strap,BiodataMiningGroup/vue-strap,lotestudio/vue-strap,tonypee/vue-strap,wffranco/vue-strap,yuche/vue-strap,lotestudio/vue-strap,wffranco/vue-strap,BiodataMiningGroup/vue-strap,tonypee/vue-strap