Allow having different pawn SP skills equipped per job

[alborrajo]

Fixes issue #327

Checklist:

• [X] The project compiles
• [X] The PR targets develop branch

DB Migration Script

DROP TABLE IF EXISTS ddon_sp_skill;

CREATE TABLE IF NOT EXISTS ddon_sp_skill
(
    "pawn_id"     INTEGER  NOT NULL,
    "job"         SMALLINT NOT NULL,
    "sp_skill_id" SMALLINT NOT NULL,
    "sp_skill_lv" SMALLINT NOT NULL,
    CONSTRAINT pk_ddon_sp_skill PRIMARY KEY (pawn_id, job, sp_skill_id),
    CONSTRAINT fk_sp_skill_pawn_id FOREIGN KEY ("pawn_id") REFERENCES ddon_pawn ("pawn_id") ON DELETE CASCADE
);