update combat_reach and bounding_radius for dragon bosses & cthun

these big bosses have really small combat_reach, so to melee them you have to stand inside them and they stand inside the tank to melee him. i just briefly checked all bosses, there are probably some more which need an update.
i found almost all correct values in the trinitydb, but eye of cthun was 1 so i had a look at it myself on blizzard servers and guessed. i also included correct bounding_radius.