Rewrite bunch analysis module?

[austin-hoover]

• Rename some methods like getCorrelation -> getCovariance.
• Move functions like BunchExtremaCalculator to the same place as BunchTwissAnalysis and BunchTuneAnalysis (currently imported from orbit.core.bunch module.
• 3D eigenemittance calculations.
• Arbitrary moment calculations (currently can only do $x^4$, $y^4$, etc.)
• Rename to something other than BunchTwissAnalysis. Twiss parameters are one parameterization of covariance matrix; this module does more than calculate those.