Reset to default Ribasim style

[visr]

With #1748, specifically 540b620, we now support preserving a customized QML style in the GeoPackage. If a users does not like their own modifications and wants to reset to the default style, that is now difficult. I think they'd have find the QML files themselves and load them and save them into the GeoPackage themselves with QGIS.

We can make this easier by providing something like model.reset_style(), and perhaps a similar option in QGIS.