Merge feature/2pncmin into next

This is the updated 2pncmin model, where the test does not pass yet! Anyhow, this is a stripped down version doing merely the precipitation related things and inherits everything else from the 2pnc-model. Since the 2pnc does not have a proper test at the moment, this should be merged and checked again once the 2pnc model is safe (and the 2p2c-test passes with the 2pnc-model).