Implement visualizing extended persistence

[rrrlw]

Potentially useful reference here

[corybrunson]

I think this is done in 14c5b6bbbf9a79309908a5bfeac154e233f869fc. Or does this issue refer to something more elaborate? Eventually some engines might compute EPH, but already the statistical transformations can handle EPH when formatted correctly—and, if it turns out that it's conventionally formatted differently, then we can update the stats.