Expose box splitting by making this algorithm a derived class of the BoxControllerSettingsAlgorithm. Also set sensible defaults for these splitting parameters. Fix the way that the workspace is created such that the box signal and error values are recalculated correctly.

Specifically, one of the ouput properies was not being set.
Unit tests checks of the output properties have been added.
The failure of the example was due to a change made by Pete in a previous ticket, but I've update the help text.

It was always logging (to debug) that it wasn't doing anything. No
it is a bit louder about it.

...in the peaks table of slice viewer.

I love working towards encapsulation.