Introduce RxScala + improve deck overlay

The refactoring to use RxScala is not complete (For instance, moving the log messages out of the HearthstoneLogMonitor is not done) but this set of commits brings some bug fixes and improvements on the deck overlay :

- resizable window
- should not mess anymore with logged events from previous matches
- remembers its last position and size like the main window

I have tested it in Ranked mode only for the moment.

It should fix #357 and #380