Fix returned promise wasn't deep enough.
Fix issue of invalid order of task's actions.

Because of the nature of promises, the callback context is not the same as the (wrapping) for loop. To fix this inconsistency, a new internally used `scope`-property `__idx` was introduced.
Implement CombineAudio task action.
Add configurations for CombineAudio; this adds sounds prepended for the main events.
Exclude all resources mp3s. Sorry about that.