tabs: fix bug in PlotTab parsing
state: re-organised module

    - SummaryState now defined in state.core
    - ALLSTATE definitions now in state.all
    - load_states now defines and readies the ALLSTATE, meaning its
      active segments are set to [start, min(end, NOW))
    - gw_summary will define the ALLSTATE manually in the event of the
      [states] section not being present