Fix hard-coded lookup tables

[mike1813]

There is an issue with the lookup tables as currently encoded in the JenaQuerierDB functions to calculate highest/lowest TW levels for an asset population, based on the average TW level and population size.

In principle, the highest and lowest TW levels in a singleton asset class should be equal to the average TW level. At present, this is not the case for the highest TW level lookup table where the number of levels in the TW scale is 6 and the number of population levels is 5.

This will cease to be a system modeller issue once we have addressed #183. It is only worth correcting the faultly lookup table if we can't address #183 any time soon.

[mike1813]

Reviewed by @mike1813 : since it is now unlikely that issue #183 will be addressed in Spderisk V1, it should be fixed by making some trivial changes in the JenaQuerierDB functions as described.