Addresses several related problems:
* Propagation / unpropagation of duplicate bonuses is inconsistent, causing bugs
* Duplicate bonuses never stack, which is not always intended behaviour (e.g. multiple copies of resource generating artifacts)
* Different bonuses always stack, which is not always intended behaviour (e.g. Angel + Archangel morale bonuses)
This is addressed as follows:
* Duplicate bonuses are never eliminated during propagation/inheritance.
* Unpropagation eliminates only a single copy of duplicated bonus
* Bonus receives a new field stacking that determines stacking behaviour:
* * empty string = no stacking with duplicates (default)
* * "ALWAYS" = stacks with duplicates & everything else
* * some other value = no stacking with bonuses with same stacking value
Also Morale/Luck window now hides non-stacking bonuses.
* Indirect spell effects loading
* Json serializer improvements
* spell->canBeCastAt do not allow useless cast for any spell
* Added proxy caster class for spell-created obstacles
* Handle damage from spell-created obstacles inside mechanics
* Experimental GameState integration/regression tests
* Ignore mod settings and load only "vcmi" mod when running tests
* fixed https://bugs.vcmi.eu/view.php?id=2765 (with tests)
* Huge improvements of BattleAI regarding spell casts
* AI can cast almost any combat spell except TELEPORT, SACRIFICE and obstacle placement spells.
* Possible fix for https://bugs.vcmi.eu/view.php?id=1811
* CStack factored out to several classes
* [Battle] Allowed RETURN_AFTER_STRIKE effect on server side to be optional
* [Battle] Allowed BattleAction have multiple destinations
* [Spells] Converted limit|immunity to target condition
* [Spells] Use partial configuration reload for backward compatibility handling
* [Tests] Started tests for CUnitState
* Partial fixes of fire shield effect
* [Battle] Do HP calculations in 64 bits
* [BattleAI] Use threading for spell cast evaluation
* [BattleAI] Made AI be able to evaluate modified turn order (on hypothetical battle state)
* Implemented https://bugs.vcmi.eu/view.php?id=2811
* plug rare freeze when hypnotized unit shots vertically
* Correctly apply ONLY_MELEE_FIGHT / ONLY_DISTANCE_FIGHT for unit damage, attack & defense
* [BattleAI] Try to not waste a cast if battle is actually won already
* Extended JsonSerializeFormat API
* fixed https://bugs.vcmi.eu/view.php?id=2847
* Any unit effect can be now chained (not only damage like Chain Lightning)
** only damage effect for now actually uses "chainFactor"
* Possible quick fix for https://bugs.vcmi.eu/view.php?id=2860
