More Generic Layers2Pressure Class

[timothyas]

There were a couple of issues with the Layers2Pressure module/class:

1. It only worked with the UFS vertical grid (127 vertical levels etc)
2. It uses "level" as the label for the vertical coordinate, not "pfull", which is what FV3 calls it

This PR addresses both of those issues. Some outstanding issues though:

• either remove or finish off the commented code at the bottom, which starts to implement the pfull/level renaming
• update the jupyter notebook documentation
• bump version