Fix config to save checkboxes values when they are unchecked (false)

In settings.cfg we must store if a preference is enabled(true) or disabled(false).
Given the fact that checkbox are not serialized when unchecked, this trick allows us to set them as 'false'.

We can think about the possibility to move that piece of code directly in the config class but we must know which language (javascript/python) to use to save the value. Currently for the editor section I use javascript, namely the unchecked value is set as 'false' instead of 'False'.