Add example for date_field

[lcreid]

As mentioned in #762, the formatting of date_select, time_select, and datetime_select is dependent on the bootstrap_form SASS. And input field of the appropriate type is probably a better solution nowadays, showing a date or time picker.

This PR adds an example of date picker, and in the process updates the compose.yml to use a sensible date format.

May partly address #762.