De-select default value for Select component

[robinmolen]

Currently, when selecting a default value for the select component, you cannot undo the default value selection (mean, if you choose to not have a default value, you cannot (easily) de-select it)

This is only a 'issue' for when the multiple configuration is set to False.

Steps to repeat:

1. Set data source to "Manually fill in"
2. Make sure that multiple values isn't checked
3. Define values
4. Define the default value

Possible solution

Maybe add a "cross" icon when a value is selected, and when you click it it sets the value to empty?