Sensitive formwidget: add getLoadValue() method

[mjauvin]

Fixes #1321

[mjauvin]

I added a sensitive field to the Winter.Test plugin here to help with this: wintercms/wn-test-plugin@eacde47

[mjauvin]

I might have found a way to fix this in the Sensitive formWidget itself, but I need to be able to access the model's data and I'm missing something...

I need to override the getLoadValue() method of the Sensitive formWidget in order to fetch its value from the model data directly instead of its data.

[mjauvin]

@jaxwilko can you test this fix ?

Feel free to provide feedback.

[LukeTowers]

@mjauvin I'm going to have to take a stab at fixing this myself, a FormWidget shouldn't be reaching directly into a model to grab a value, there's too many assumptions there that could go wrong.

[jaxwilko]

@mjauvin I tested and this does work :)

[mjauvin]

@LukeTowers the RecordFinder formwidget does this as well.