Added antibanish mechanics: as like other "diseases" that can be treated
with some useable items, banish will be able to be recovered as well.
Fixed some SQL issues introduced on the last commit, as well as
lingering inexistent ids on drop data. Fixed some concurrency issues
with MapleMapFactory. Set a ceiling for simultaneous items available per
map, where old ones are promptly discarded. Patched MWLB attack block
for higher level GMs.
Fixed performance drop on the server when trying to level up equipments
which has high stats points. Added a flag enabling massive damages with
Three Snails skill.
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).
