axiomlib: improvements in fuzzymultidataext.axstagetree

Signed-off-by: Victor Shcherbinin <victorshch@gmail.com>
axiomlib: added parameter entropyObjective to fuzzymultidataext.ecstage

If entropyObjective=true, objective function based on entropy is used instead of objective function based on frequencies fraction. Also ECs are automatically negated during training, so the algorithm does not need to separately train on negated EC types

Signed-off-by: Victor Shcherbinin <victorshch@gmail.com>