Resolve "Component MultipleSelectField fails to properly select filtered items"
Closes #1 (closed)
Refactored the component MultipleSelectField. A new component, CheckboxListMenuItem, was created as an intermediate between MultipleSelectField and CheckboxListItem. Whenever an item is toggled, CheckboxListMenuItem handles the toggle event first and sends the actual item, rather than the event, to the _handleToggleCheck method in MultipleSelectedField. This removes the need to lookup the toggled element inside the menuItems property.
The new folder structure:
