Ability to automatically set podcast as listened

Ability to automatically set podcast as listened after successfully sending it to a device.

It's a wip. Need feedback.
Add a signal to `OrganiseDialog` called `FileCopied(int)` and change this to:
```c++
connect(organise, SIGNAL(FileCopied(int)), this, SIGNAL(FileCopied(int)));
```
Then connect to `OrganiseDialog`'s new signal from `PodcastService`