3D plot tests, plot test suite fixes and rcParams fix

[GiudGiud]

This PR addresses issues #460, #304 and #297 .

• the similarity criterion for comparing plots to the expected result in the test suite is tightened
• a bug with overlapping title and suptitle is addressed by using constrained layouts
• matlplotlib's current rcParams will be modified by the plotter instead of the mpl defaults
• a set of 3D plots test is added
• all plots test are updated because of the overlap fix

[coveralls]

Pull Request Test Coverage Report for Build 1024

• 14 of 14 (100.0%) changed or added relevant lines in 2 files are covered.
• 85 unchanged lines in 3 files lost coverage.
• Overall coverage increased (+1.04%) to 80.203%

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Files with Coverage Reduction	New Missed Lines	%
tests/openmoc/openmoc/materialize.py	1	73.82%
src/Mesh.cpp	2	40.7%
tests/openmoc/openmoc/plotter.py	82	88.97%

Totals
Change from base Build 1014:	1.04%
Covered Lines:	13219
Relevant Lines:	16482

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💛 - Coveralls