first version of desktop JAR assembly using proguard

It still needs some work, probably better filtering of backend (we just include everything) and some fixes to possible bugs due to:

    [info] Note: there were 3 unresolved dynamic references to classes or interfaces.
    [info]       You should check if you need to specify additional program jars.
    [info] Note: there were 14 accesses to class members by means of introspection.
    [info]       You should consider explicitly keeping the mentioned class members
    [info]       (using '-keep' or '-keepclassmembers').

but first 3 are from javax.jnlp and seems to be not essential, and introspection warnings are not critical I think.

For my simple test project (pong) I've got jar file that was 6.2mb instead of 16mb, so almost 10mb was cut and game still works nicely.