Reworked and fixed selection of secondary skills:

- Fixed off-by-one error when checking for obligatory skills
- If both wisdom and magic school must be offered in the same slot, magic
school will be correctly offered on next levelup
- Obligatory skill can now be proposed for upgrade
- Obligatory skills are now offered using hero class weight instead of
simple random
- If hero has multiple skills not available to his class game will
select random skill instead of first one
- Moved storage of random seed to server instead of mutable member

server/processors/HeroPoolProcessor.cpp

@@ -351,6 +351,17 @@ CGHeroInstance * HeroPoolProcessor::pickHeroFor(bool isNative, const PlayerColor
 	return *RandomGeneratorUtil::nextItem(possibleHeroes, getRandomGenerator(player));
 }
 
+CRandomGenerator & HeroPoolProcessor::getHeroSkillsRandomGenerator(const HeroTypeID & hero)
+{
+	if (heroSeed.count(hero) == 0)
+	{
+		int seed = gameHandler->getRandomGenerator().nextInt();
+		heroSeed.emplace(hero, std::make_unique<CRandomGenerator>(seed));
+	}
+
+	return *heroSeed.at(hero);
+}
+
 CRandomGenerator & HeroPoolProcessor::getRandomGenerator(const PlayerColor & player)
 {
 	if (playerSeed.count(player) == 0)