Aggregate scores calculated on techniques with no sub-techniques

[clemiller]

Aggregate scores are being calculated and assigned to all parent-level techniques with scores regardless of sub-techniques, which causes inadvertent behavior when the "non-aggregate score color" option is disabled (feature introduced in #538). Techniques with no sub-techniques are still colored according to the hidden aggregate score they have been assigned. Aggregate scores should only be calculated on techniques with sub-techniques; all other techniques should remain "unscored". When factoring aggregate scores into sorting, prefer techniques scored 0 over unscored.

[clemiller]

Changes staged on develop.