Add bootstrap-datetimepicker

The files have been obtained straight from the repo tag:

* https://github.com/tarruda/bootstrap-datetimepicker/raw/v0.0.11/build/js/bootstrap-datetimepicker.min.js
* https://github.com/tarruda/bootstrap-datetimepicker/raw/v0.0.11/build/css/bootstrap-datetimepicker.min.css

Thanks for all your work!