[IMP]Improved the many2one widget, added model as property of widget, model will be the backbone model, widget will use that model to get result for name_search, used backbone so that we do not need to store projects and tasks explicitly because we already having data inside model, also we do not need to bother about retrieve task of selected project, when user selects project we will set that project model as a property of task m2o and when name_search is called for task m2o it will return names of task collection. Also added the logic to remove activity.