feat(carousel): no-wrap attribute

Hey,

I wonder how to implement impossibility to wrap carousel around (i.e. user can't move it back when there's first slide and can't move it forward when there's last slide). This is possible implementation.

P.S. Implementing this I found a problem with and old test 'should hide navigation when only one slide' for carousel. 
If I change scope.slides=[{active:false,content:'one'}]; to scope.slides=[{active:false,content:'one'}, {active:false,content:'two'}]; test doesn't fail. I tried to add another $apply() call but it doesn't seems to work so I leave it as it is.

Thanks