Develop

The last of the three commits adds the `autoSort` argument for `XYSeries`. For me it's quite crucial to be able to turn off auto sorting, because I'm using scatter plots with a custom item label renderer based on the item index (which gets scrambled in auto sorting).

The first two commits just add a .gitignore file, sbt version info, and put the source files into the package sub folders (default layout I think for most setups, e.g. IDEA), I hope this is fine (if you dislike that, one can probably undo the middle commit).