Update strategy for reference energy bins in particle flow

The current code contains an unusual way to access energy bin indices. Although this can make sense, to some extent, if looking up indices using the mid point of low and high bin values we decided for the future to migrate to a strategy of simply using the low bin edge to compare to energy value to determine bin index.

This change would not be compatible with current e/p reference files in use in production and so the relevant functions are migrated to "legacy" versions in use by default. Future e/p reference files will not use this legacy option access method.

Furthermore another legacy option to toggle how we do the bin lookup, which has not been used for a very long time, is also removed. Legacy code related to eflowTauTool has also been removed, which was spotted whilst making the updates for this MR.

No changes in output are expected.