Verbosity improvements

[RobinD42]

Fixes #1362
See also NanoComp/mpb#125

• Make it possible to access the individual verbosity levels by name in the Verbosity class
• Switch verbosity checks in Python code to verbosity.meep or verbosity.mpb
• Make MPB's version numbers be accessible from Python in the meep.mpb package
• When calling mpb code from meep code set mpb_verbosity to meep::verbosity - 1
• Switch most mpb_verbosity checks to >=1, to be closer to the original intent of the new verbosity functionality
• Added a unit test module for testing the Verbosity class

[RobinD42]

NOTE: After playing with and testing this change for a couple days I'm not so sure that the feature of setting mpb_verbosity to meep::verbosity - 1 won't cause more confusion than it's worth. Maybe it won't happen often in real life usage, but it took me several minutes to realize why this wasn't working, and I'm the one who made the change:

verbosity.meep = 2
verbosity.mpb = 3
a_solver.run_te()

Since the mpb_verbosity was set to 1, I didn't see the messages I was expecting.

[stevengj]

After playing with and testing this change for a couple days I'm not so sure that the feature of setting mpb_verbosity to meep::verbosity - 1 won't cause more confusion than it's worth.

It should only be done in src/mpb.cpp, i.e. when MPB is called from Meep, and not when you are calling functions from pympb like run_te().

[RobinD42]

Okay. I've reverted the applicable changes in pympb.cpp