Add maptier

[moemoequte]

• native int Influx_GetCurrentMapTier();
• add !settier command for admin so that admin can set current map's tier
• add maptier column using

CREATE TABLE IF NOT EXISTS inf_maps (
    mapid INTEGER NOT NULL AUTO_INCREMENT PRIMARY KEY,
    mapname VARCHAR(127) NOT NULL UNIQUE,
    maptier INT DEFAULT 0
);

[TotallyMehis]

Good job. I'll merge in a day or two.