Implement Steam Unified

[LossyDragon]

Description

Throwing this here as an initial start to see if any eyes looking at this can maybe help improve this.

I managed to tinker around and get a working implementation of Steam Unified Messages.

It seems Java lacks some features compared to C# (SteamKit) to do some reflection magic to get the calling method within lambda, among other things possibly (or that I lack skillset wise), to cut down on some boilerplate.

Example, Steamkit can extract the a method call from a lamba, in which sendmessage passes down to be extracted, then uses reflection to build it all neatly in one method.

// C#
var playerService = steamUnifiedMessages.CreateService<IPlayer>();
playerService.SendMessage( x => x.GetGameBadgeLevels( req ) );

vs

// Java
Player playerService = new Player(steamUnifiedMessages);
playerService.GetGameBadgeLevels(badgeLevelsRequest.build());

After a few weeks of trying anything that I've learned, it appears Java cannot do it, so we have to make an adapter class to implement IPlayer, and pass everything though there.

However; building the Unified Message directly is on par with Steamkit, so thats a plus! :)

steamUnifiedMessages.sendMessage("Player.GetGameBadgeLevels#1", badgeLevelsRequest);

The interfaces need to be changed to return JobID, which is no biggie, while the "adapter" classes need to be built manually or generated with a groovy script

Checks off Steam Unified in #181 as the functionality is implemented.

Checklist

• Code compiles correctly
• All tests passing
• Samples run successfully
• Extended the README / documentation, if necessary