fix "Assert #74 failed in aria.core.Timer" in test launcher

I'm not sure about it. Probably more often than not when someone adds a callback he would like to have the proper `scope`.

I think we should replace [$assert](https://github.com/ariatemplates/ariatemplates/blob/v1.6.9/src/aria/core/Timer.js#L118-119) with `$logError` in case of `cb` or `cb.fn` being `null`, and `$logWarn` if `scope` is `null`. It might be annoying to have the warning for empty scope, but it's like JSHint complaining about certain things that usually fine but can lead to errors. Moreover if anyone is using callback without scope, he already has assert red errors from Timer, so it will not flood anyone's console, just turn errors into warnings.