Merge pull request #205 from fragmer/master

Code quality improvement batch #2 (Minecraft$OS refactor, dead code removal)
Fixed a number of bugs and inefficiencies in ResourceDownloadThread. Now the client can start normally in applet mode or from launcher, even if some resource files were missing. TODO: proper threading/synchronization with main thread, to avoid locking up the UI during download.
Cleanup in Minecraft: reduced resource leaks, improved download speed/reliability for images, thoroughly documented onMouseClick()
Merge branch 'master' of github.com:andrewphorn/ClassiCube-Client