hello github!

First release on github.

• Licence is now GPLv2.
• Everything is now packaged in a single jar file.
• overhauled the organisation of the local SVN working copy: it's now rooted at the top of the Scenery directory with depth EMPTY; individual tile subdirs are sync'd when needed.
• Models and Airports directories now supported.
• Models are sync'd using a new button on the toolbar.
• When syncing a scenery tile containing airport codes, the corresponding Airports/?/?/? directory is also sync'd.