Add the option to save game results to a local JSON file

File export is disabled by default. The export directory defaults to the user's home directory. Local file saving doesn't replace uploading to track-o-bot.com, it's just an additional output option. The trackobot.com upload is always enabled.

Some notable changes to the codebase:
* Create IResultSink interface to allow for multiple receivers of game results.
    * Tracker and LocalFileSink both implement IResultSink
    * Core stores pointers to all ResultSinks in a QHash, reports game results to all of them. 
* Encapsulate game result information into the Result class.
* Move Result-to-JSON work from Tracker to Result::AsJson()

File export options UI:
![screen shot 2014-09-24 at 8 21 39 pm](https://cloud.githubusercontent.com/assets/3039654/4399127/168d6708-4463-11e4-995c-e4a84abfce0c.png)