Update Camels notebook example to use "TAG" field & variable start and end years

[edwardchalstrey1]

• Liase with Seshat team to understand the values for this field

  •   Tags = (
      ('TRS', 'Confident'),
      ('SSP', 'Suspected'),
      ('IFR', 'Inferred'),
      )
    

• Update the notebook to factor this in

• Also factor in that some absent/present variables have start and end years for the value within the polity year range, i.e. the value can change from absent to present