pv_atmos: Logarithmic and reverse coordinates in any direction

When loading the data with LoadData(), one can now define any dimension as a logarithmic dimension with independent basis. Another new feature is that every dimension can be reversed now, independently of whether or not it's a logarithmic coordinate.

There is also a fix for the use of pv_atmos without proper installation. The test functions and examples now ask for the path to pv_atmos instead of assuming one specific location. When asked, provide the path to the location of the basic.py and grids.py, i.e. including the pv_atmos folder, e.g. /home/usr/pv_atmos