Split/rearrange package structure

[pont-us]

As of [2018-10-08 Mon], there are 43 top-level classes in the data package. This is a bit much. FileType and CsvWriter might be better off in data.file, but that won't slim data by much. I think the best plan is to create a data.calculation (or maybe just puffinplot.calculation, or calc, or calcs) package, which could reasonably contain:

• ArasonLevi
• ArmSampleRpiEstimate
• Eigens
• FisherParams
• FisherValues
• GreatCircle
• GreatCircles
• KentParams
• MagSusSampleRpiEstimate
• MedianDestructiveField
• PcaAnnotated
• PcaValues
• RpiEstimateType
• SampleRpiEstimate
• SuiteCalcs
• SuiteRpiEstimate
• Tensor
• VGP

That would be 18 classes in the new package, leaving 16 in data.

Also consider a puffinplot.util package, into which Util, IdToFileMap, RecentFileList, and Version could be moved.

window has 30 classes. It should probably be renamed swinggui, and split up into "window" and "component" subpackages. Once PuffinApp is split up, the gui bits should go here too.