Update for Essentials API change

In 2.12.1 and newer version, method parseStringMeta in com.earth2me.essentials.MetaItemStack is expecting net.ess3.api.IEssentials rather than com.earth2me.essentials.IEssentials.

This will break compability with older Essentials-version (pre 2.12.1), but will allow users to utilize newest Essentials-version.