Proposal: move BunchExtremaCalculator to orbit.bunch module

Proposal to move [BunchExtremaCalculator](https://github.com/PyORBIT-Collaboration/PyORBIT3/blob/main/src/utils/bunch/BunchExtremaCalculator.cc) to the same place as `BunchTwissAnalysis` and `BunchTuneAnalysis` (currently imported from `orbit.core.bunch` module.