Efl.Ui.Mutli_Selection needs to be implemented on Efl.Ui.Collection_View.
Information about the selection state however needs to go into the selection model.
- The selection state of the items that are on the screen is tracked via the event, change to the `selected` property are applied to the selection state.
- API calls of the mutli_selection are called on the selection model.
- If one of the models on the screen changes its selection change, this needs also to be applied to the item on the screen.
- The API of the iterator is moved to another interface called Efl.Ui.Multi_Selection_Sync, the selection model can provide its own async way of providing this information.
- Selection model can just keep the last slected model arround to be accessed synchronisly, which makes the usage of the Single_Selectable interface quite easy.