JSON-RPC: Add playcount to "AudioLibrary.setSongDetails" and scrobble-like options

With addons like chorus for the web interface and yatse as an android application streaming from kodi to our pc/smartphone has become a real fact. I've been a few months guessing how can I simply synchronize my phone playcounts with kodi, just for having some dynamic playlists that really work despite not listening music on my media center. I found nothing.

So after starting to build my own webinterface, I realised that there's no "playcount" in "AudioLibrary.setSongDetails" method. Is there any reason for not adding this option? Because I've seen you can update the playcount on tvshows and movies.

As a second idea (for me it would be perfection), I would propose adding some extra methods to the AudioLibrary in the JSON-RPC api: AudioLibrary.scrobbleSong (maybe album too). These methods simply increase the playcount of the given element and update the lastplayed to the current time.
You need to use
```
song.lastPlayed.SetFromDBDateTime(parameterObject["lastplayed"].asString());
```
here. Does this even compile right now?