Test pivots end to end and record their golden screens

An e2e test builds a pivot through the editor, is refused an edit to
its results, follows its source, survives save and reopen, and cancels
an edit with Esc; another makes a frequency table. New screens: the
pivot editor (also at 60 columns), a pivot, its filter picker and a
frequency table, dark and light. The palette and shortcuts goldens
change with the new commands. The pivot editor keeps a line's first key
hint when the status line is narrow, and the frequency command is named
Frequency table (column stats) so Data's C still runs Create a filter.

commit

5919132da81eacdbb4a9036992d40589eebd8307

parent

4f28187e0b2848071623a1423aec6ca905a9b71a

author

Dami <dami.etoile@gmail.com>