Adding functionality for importing and exporting new csv model files with metric and slice transformations

[flemingjf]

Since toxpiR has increased functionality over the ToxPi Gui, allowing for both metric transformations and slice transformations, as well as different ways of handling negative data and rank ties, a new csv model format should be made that is compatible with the new functionality. This will make sharing models with data easier and more reproducible. These files will not be backwards compatible with the GUI.