feat(scope/timers): add $timeout and $interval methods to scope

Intervals and timeouts created with scope’s methods will be automatically destroyed
when the scope is destroyed, thus preventing memory leaks.

If controllers and directives use scope.$interval and scope.$timeout instead $interval and $timeout, there is a lower risk of memory leaks, as there is no need to remember to cancel the promises of the timers.

This is not extrictly needed but may be useful.