Updating `DMCSimulationResults`.

Making 1 the default `final_result_index` if no result files are found.
This allows the class to be used to parse result summary files if no raw
result files are present.
Adding `almost_equal` function to `stats` module.

Adding simple function for comparing floats for equality.
Debugging histogram support in `plotting`.

Adding `Ticks` class for holding ticks and tick labels settings.
Instances of this class can be stored in `ScatterPlot` to allow
ticks and tick labels to be reproduced faithfully when plots are
reset.

Also adding x and y limit attributes to `ScatterPlot` so that the
limits can be reproduced on resets.

Working on debugging `PsiPowerPlotGrid` class.