Allow to pass label as `node` into form elements

[mbohal]

We need to add the possibility to pass either string or node into the label prop of form field components.

This is due to a requirement to use the label as a trigger for showing a Popover component.

Change needs to take place on:

• https://react-ui.io/components/CheckboxField/
• https://react-ui.io/components/FileInputField/
• https://react-ui.io/components/Radio/
• https://react-ui.io/components/SelectField/
• https://react-ui.io/components/TextArea/
• https://react-ui.io/components/TextField/
• https://react-ui.io/components/Toggle/