Widget editables allowedContent does not filter correctly

[Kristiaan Van den Eynde]

Steps to reproduce

1. Create a widget plugin called "justData"
2. Set its requiredContent to:

'div[data-my-attr]'

3. Create a widget plugin called "dataAndClass"
4. Set its requiredContent to:

'div[data-my-attr](my-class)'

5. Create a widget plugin called "containerForDataAndClass"
6. Add an editable field to the widget
7. Set the editable's allowedContent to:

'div[!data-my-attr](!my-class)'

8. In the actual editor, create a "containerForDataAndClass"

Expected result

I can only add a widget of type "dataAndClass" in the container

Actual result

I can add both a widget of type "dataAndClass" and "justData" in the container. When switching to source view and back, the "justData" widget code is removed, however, as it does not match the allowedContent for the editable.

In summary

I can use a button that I should not be able to use inside of the editable ("justData")

[Tade0]

Bug occuring since 4.5. Attached the implemented widgets so that the person dealing with this bug doesn't have to start from scratch.