Implemented TempActor bound to a TempContainerActor

This is my attempt to fix some usability problems I see in the current `TempActor` impl:

 * each time you use TempActor you have to pass a reference to another actor where to spawn it from
 * the temp actor doesn't stop when it gets it's reply
 * it should be possible to timeout the temporary actor.

About the timeout issue: it would be straightforward to write with the current TempActor impl:

```python
temp,d = TempActor.make(parent)
target << ('something', temp)
res = yield with_timeout(1.0, d)
```

This will work, but the temporary actor will stay alive forever and leak resources.