fix Biome names + SQL exception

it was calling `toString` on Biomes at a few places, which returned the whole package name, e.g.
`com.worldcretornica.plotme_core.bukkit.api.BukkitBiome@deadbeef`.

That also resulted in SQL exceptions since the string is longer than the biome column (varchar 32).

This PR should fix that and show the actual Biome name. Thanks to @dico200 again for some help.