tabs.registry: added registry of tabs

    - SummaryTab is now default
    - Allows addition of HvetoTab and DailyIhopeTab classes in future,
      for example
modularity! updated plots and tabs to be modular

    - registry now works properly for tabs, in prep for Hveto and
      DailyIhope input
    - reworked plotting code, just for the lolz.