Rework item damage output calculation

[NeumimTo]

Class Damage = merged damage value from classes/races, either sum, or max
additionally there should be one more configuration option which will cover states where a player has item in hand having additional item attribute generic.damage

• IGNORE - generic.damage value will be ignored and Class Damage will be prioritized (=current implementation)
• OVERRIDE - overrides Class damage if present on an itemstack
• SUM - Class damage + generic.damage
• MAX - damage = max(Class damage, generic.damage)

[NeumimTo]

#137 - random damage ranges

• On spigot add support for mmo items