Create repo with PSDM grid data

[johanneshiry]

At the moment, the test folder contains only very small sample test grids which may not be very useful for extensive testing or production runs. However, having at least 2-3 standard grid models which cover most of the features of the PSDM and serves as "up-to-date" blueprint of some grid models.

As these models may also be useful for integration tests of PSDM one may consider putting them either in the test folder or in a separate repo