Added mechanics for the EXP/DROP cash coupons (such as enabling
out-of-time active coupons via command and automatic update of active
ones over the designed interval). Created MapleCouponInstaller as means
to gather info about the coupon intervals and rates from the WZs (the
generated SQL table is already updated on the db_database.sql file).
Made NPCs now work properly on multiworld system. Solved multiple issues
regarding Player Shops not giving back items properly when owner exits.
Added restriction on changing channels at FM rooms, preventing shop
owner entering Cash Shop.