[0.29.0] Skill system improvements

[Chnossos]

The skill system has been updated with a major change!

Previously, there were two big limitations:

1. All skill effects were directed to the targets, meaning it was not possible to apply an effect to the caster;
2. Targets were decided at the skill level, not the effect level, meaning that all effects shared the same list of targets, all the time.

Now, each effect has its own EffectTargetType AND SkillTargetNature properties: you could make up a skill to have an effect that targets the current target, then another effect that targets the surrounding summons, then a third one that heals the caster, its party and all the surrounding friendly characters around him!

You can become very creative with this.

Take note that there's a serious visual gameplay limitation: the game client cannot display multiple effects that target multiple targets. In other terms, if we were to implement the imaginary skill I described above, you couldn't have three different visual effects to display depending on the effect's targets.

So, in the new implement I made, the first effect gives the spell its visual targets and effects. If you want you skill to visually target multiple opponents, then make sure its first Effect is an AoE one!

[Chnossos]

@targun123 Here you go. Aura Flare is kind of already implemented in this version (there's no pvp-related stats yet but you could easily add your own).