Implement AudioInputStreamWrapper for AmazonPollyCacheWrapper

[ewjmulder]

        // TODO: idea: to realize the long dreamed ideal of having a direct streaming from Polly to Immerse playing, this caching
        // step is the last hurdle. But just as the Immerse idea of caching while playing, we could do that here as well.
        // Details: have some kind of (audio) input stream wrapper that forwards bytes read to another output stream,
        // in this case the cache file. In case of stopping before EOF, the cache entry should be deleted. (or rather, never stored)
        // Update: this mechanism has been implemented in Immerse and is working, see AudioInputStreamWrapper!