Update MetPy Case Study to use MetPy v1.0 API and features

[jthielen]

As revealed by this StackOverflow question the MetPy Case Study workshop notebook uses out-of-date API for mpcalc.advection (like #125), but also has a now-horrifying amount of boiler-plate code for things cleaned up with xarray handling in v1.0. So, I think this notebook could use a good update or overhaul!

xref (for other updates I could find in issue tracker): #44, #81

[jsillin]

I also found this to be the case (at least with regards to using the outdated Metpy Calc API) in the Frontogenesis example https://unidata.github.io/python-training/gallery/850hpa_frontogenesis/