Update src/js/bootstrap-datetimepicker.js

When using the datetime picker in a form that uses the class 'form-horizontal', there is extra HTML that must be added around the form fields.
The default behavior would cause issues with the layout and cause the input to forced down, and out of alignment with its label.
I updated the code to not only look at the current element for 'input-append' or 'input-prepend', but in the element's parent as well.