Arthritis checkboxes validation (allow false)

[ashleybot]

When the domain property is null or 0 then the view model property should be mapped to false, and vice-versa.

When the domain property is 1 then the view model property should be mapped to true, and vice-versa.

This allows for easily rendering checkboxes and for the appropriate values to be mapped in both directions. Before this fix, the model would not allow implicit conversions for false.

[ashleybot]

@smiththay Please take a look at my PR. The D1 also has several checkboxes that we'll need to update when the time comes.

[smiththay]

@ashleybot Functions the way it should

[ashleybot]

Thank you @smiththay