Fix for count of tasks update value & generating simple id for new tasks

Only two cases, not valid reason for creating a watcher, so this was my
approach. To modify the $scope.cont variable whenever it changes, adding or deleting a task/tasks
You're absolutely right. 
Though that brings a couple of questions, does the todo-list project intent to add more functionality? If so, will the task have multiple states that may affect the total count of tasks? knowing this is what we visually show to the user as the total amount of taks in the list.

We are assigning the length of the $scope.taks Array to the $scope.cont variable. Even defining an empty Array will make cont as 0, this will never get an error, and we can use simply the increment and decrement operators alone to change the count whenever a task is added or deleted.