Allow the datetimepicker widget to be embedded as a standalone component

This patch adds support for embedding the datetimepicker directly as a
component (i.e. without the popup).

To use it, set "embed" to true, e.g.:

    $('#datetimepicker').datetimepicker({
        embed: true
    });

(Adding this patch solves issue #84, except for it not being the default when the component is a div, but rather an option you select.)