Initial command cleanups

[mathiascode]

Initial work on cleaning up the code style and unifying in-game and console commands.

[madmaxoft]

This approach will make it harder for us when we finally get to refactoring the console command handlers and adding command block handlers. The general idea is that the command handlers' signature will be unified into function cmdHandler(aSplit, aSource), where aSource is either a cPlayer, or a cCommandBlockEntity, cMinecartWithCommandBlock or cConsole. The current status (separate handlers) will continue working after such a change, but your changed code will try to detect console by comparing aSource to nil, which won't be true for console anymore.

[mathiascode]

I suppose we could use a wrapper approach in the meantime (such as https://github.com/cuberite/Core/blob/master/weather.lua#L37)?

[madmaxoft]

Well, the changes will be done after the big 1.13 refactoring anyway, so we can postpone until then, and merge this PR in the meantime.

[mathiascode]

I still want to add some comments to the code. Feel free to point out areas you think should have them.