Unit stack rebalancing rework

- CStackInstance::count is now private with accessor methods
- CStackInstance::experience renamed to totalExperience and now stores
total stack experience (multiplied by stack size) to reduce rounding
errors
- CStackInstance::totalExperience is now private with accessors methods
- stack experience is now automatically reallocated on stack management
- Removed buggy BulkSmartRebalanceStacks pack, that mostly duplicates
BulkRebalanceStacks
- Renamed BulkSmartSplitStack to BulkSplitAndRebalanceStack to drop
unclear "smart" in name
- Reworked split-and-rebalance logic to correctly reallocate stack
experience

lib/mapObjects/CGHeroInstance.cpp

@@ -468,7 +468,7 @@ void CGHeroInstance::initHero(vstd::RNG & rand)
 	{
 		commander = std::make_unique<CCommanderInstance>(cb, getHeroClass()->commander);
 		commander->setArmy(getArmy()); //TODO: separate function for setting commanders
-		commander->giveStackExp (exp); //after our exp is set
+		commander->giveTotalStackExperience(exp); //after our exp is set
 	}
 
 	skillsInfo = SecondarySkillsInfo();