Default choice for clickData based plots

[asnyv]

Include a default initial choice for plots that are activated by clickData to avoid empty figures.

Examples:

• Choose best correlated value as default from tornado in plugins/_parameter_correlation.py

• Choose last timestep as default for tornado plot in plugins/_reservoir_simulation_timeseries_onebyone.py

-Choose last timestep (or mid to avoid all zeros in example?) as default for histogram in plugins/_reservoir_simulation_timeseries.py