Cancellable tasks & bug fixes

1. Fix regression introduced by 4e13b24 & ba21bbb that cause misbehaviors on synchronous tasks.
2. Factor out requestAnimationFrame scheduler from Effects library and expose it via tasks instead. Having it part of Effects did not really made much sense.
3. Renamed Effects.task(task) to Effects.perform(task) as former was pretty confusing.
4. Changed API for creating cancellable tasks so they won't perform extra allocations on execution. Most relevant for requestAnimationFrame task that are used a lot during animations.
5. Change class hierarchies to avoid passing own methods to super calls.
6. Add Task.prototype.recover API so that task failures can more efficiently & intuitively be translated to error actions.