Fix #317
Fix #317

Don't delete properties anymore. Set selectedModel to {} instead.

dotansimha/angularjs-dropdown-multiselect,jjwon0/angularjs-dropdown-multiselect,jjwon0/angularjs-dropdown-multiselect,gertot/angularjs-dropdown-multiselect,dotansimha/angularjs-dropdown-multiselect,gertot/angularjs-dropdown-multiselect