Fix datetimepicker assets loading

Fixes for two bugs:

1. TbDateTimePicker would never register locate JS, for it was looking for them in wrong directory
2. TbEditableField did not load necessary scripts for 'datetime' field type ('date' field type does not require additional script loading, as its scripts are in 'bootstrap-editable.js', but scripts for 'datetime' field are in a separate package dir 'bootstrap-datetimepicker/js')