Proper clearing form field values

[tomwagner]

I think that proper way to clean forms values could be set them to undefined value:

onion-form/src/reducer.js

Line 12 in 5c7869b

value: '',

Now it's clearing to empty string, but this value can be also a user input. And in functionality of setting defaultValue to Input doesn't work correctly. There is one condition which set input fields to defaultValue only if they are undefined:

onion-form/src/connectField.js

Lines 132 to 135 in 5c7869b

	// Enable to set default value only if value is undefined
	if (typeof fieldProps.value !== 'undefined') {
	return;
	}

So for example if i have one form where some input (eg. select) has defaultValue and i clear this form by action clearForm it clears all values in state with empty string, but default value of this select won't be set because of condition above.