Proguard : reduce the size of the binaries

[tyrcho]

DO NOT MERGE AS IS !
I'm creating this PR to start the conversation

I've been trying to integrate Proguard to reduce the size of the downloaded executable, to no success at the moment. I lack experience with Proguard to fix it.

If anyone want to give a hand on this he is very welcome !

[gtch]

I think a useful step in making Proguard work will be to get rid of the code in Config.programHelper() that instantiates classes using strings, because tends to confuse tools that do compile-time analysis like Proguard.

I actually started on that last weekend in my branch config-cleanup but I haven't yet finished it. That branch moves the code in net.hearthstats.Main to two classes — one for Windows and one for OS X — which means that dependencies can be resolved at compile time instead of runtime. I should finish that off in the next few days... and it should be easier to get Proguard working once that is done.