datepicker bootstrap

remove old jquery datepicker and replace it with a bootstrap one.

Notes:
- Had to add custom modification to the library to support the weeks number.
- The bootstrap datetimepicker library need moment.js in order to work
Meanwhile, moment.js has released version 2.8.1 with [bugfixes, locale bugfixes, performance improvements and new features](https://github.com/moment/moment/blob/develop/CHANGELOG.md) but also incompatible changes and deprecations so I don't know if we should upgrade or not.