UI rework

[mplatzer]

Controls:

• dataset dropdown: cdnow (default), donations, grocery (add these to the package)
• model dropdown: ParetoNBD, BG/NBD, MBG/NBD, MBG/CNBD-k
• (optional) setting of the calibration period

Tabs:

• Descriptive Summary Statistic:
  • see #2
  • https://github.com/mplatzer/BTYDplus/issues/34
• Cohort Level Analysis
  • report estimated parameters - mean(lifetime) - mean(itt) - mean(palive)
  • plot tracking incremental & cumulative weekly
  • plot freq and recency vs holdout transactions see https://github.com/mplatzer/BTYDplus/issues/35
  • plot distribution of P(alive)
• Customer Level Analysis
  • mean absolute error & bias
  • top 5, middle 5, bottom 5 as CBS tables, with estimated columns add and highlighted (palive, xstar_estimated, sales.avg estimated, sales_estimated) - sorted by sales_estimated or by xstar_estimated