Fixed errors

Fixed the next errors
- a syntaxis error makes the application crash

- adding a todo item causes an error to be shown in the console

- destroying a todo causes an error to be shown in the console, but the
todo
disappears when the page get refreshed

- when you try to complete a task, it counts in the "items left"
counter, but it
doesn't get marked as completed

- the left item count shows incorrect number

- the clear completed button doesn't work