Added logback for basic debug logging.

Current intended for my own use… might add it upstream if it proves
useful.
Fixed auto updater for OS X

The automatic updater wasn’t working on OS. This was raised in issue
#136 and was probably the cause of #157 and #169.

I’ve made the following changes to fix it:
* Updated the OS X build to create a smaller updater.jar with a
necessary library that was previously missing
* Added a hearthstats.location property to the updater.jar call (for OS
X only) so that it knows where to find HearthStats.app
* Added full path to java.home to the updater.jar call (for OS X only)
so that the updater gets run by the same version of Java as
HearthStats.app
* Changed the unzip process to correctly handle subfolders (the OS X
bundle contains a number of subfolders not present in the Windows
version)