Merge branch '174-miscs' into 'master'

Miscs

1. Bring back the fix: The duration of an existing effect will not be reduced by setting a new effect with a shorter duration (controlled by on_merge for some  effects).
2. Living lightning correctly works with Range Amplification Device
3. Stormshield rune's block number and threshold should be an integer
4. Randart bows & slings should not have base damage

See merge request !771