buffs applied based on weapon, several skill/buff changes

[nitrogenetica]

1. Changed selfbuff logic to apply only selfbuffs for correct weapon type. Includes shields in offhand.

2. Several updates on skills/buffs
   Assist

• Replaced "Power Fist" with "Moon Beam" for support assists
• Added preselect "Avalon Shield"

Mercenary

• Added "Smite Axe", "Axe Mastery" and "Protection" buffs
• Replaced "Shiled Bash" with "Slash"
• Added preselect "Avalon Shield"

Blade

• "Spring Attack" hits 5 times
• Added "Blazing Sword" buff
• Added "Protection" buff

Jester

• Added "Enchant Blood" and "Enchant Poison" buffs, so players can free select which one shall apply
• Added "Perfect Block" buff

Ranger

• Removed "Yo-Yo Mastery" buff
• Added "Perfect Block" buff

Billposter

• "Belial Smashing" hits 5 times
• Added "Stone Hand" buff

Knight

• Added "Blazing Sword" buff

[Frostiae]

Thank you for the PR!
Now that we don't actually use constants.skills anymore, do you mind removing those changes?