add PartnerSkillLevelMultiplier

[erwan-joly]

from opennos PartnerSkillLevelType.F => 0.3D,
PartnerSkillLevelType.E => 0.5D,
PartnerSkillLevelType.D => 0.8D,
PartnerSkillLevelType.C => 1.0D,
PartnerSkillLevelType.B => 1.2D,
PartnerSkillLevelType.A => 1.5D,
PartnerSkillLevelType.S => 2.5D,