Better support for readonly attribute for selectOne and date view types

[chrisala]

Currently readonly/computed applies the readonly to the select rendered by selectOne.
The HTML readonly attribute isn't supported by select and the advice is to use disabled instead. However this prevents validation from working correctly, which you might want if the computed value needs to be validated somehow.

Similarly, the input field and button rendered for a date data type doesn't support the readonly attribute well - it still allows clicks and date selections.