Rotation and geopackage support

[ViperMiniQ]

Plugin divides the same geometry in different ways if it is rotated differently across the attempts. Rotation can now be performed prior to dividing the layer.

Also, support for GeoPackage (.gpkg) is added (issue #21 ). ESRI Shapefile is still available and set as default driver when opening File Explorer.

[jonnyhuck]

Thank you very much for this - I'll get it merged ASAP.