A separate permission for allowing the /back command to be used on death

[Jakubk15]

essentials.back.ondeath in EssentialsX

Two Position objects will be stored in a cache with configurable expiry time?. One will refer to last graceful teleport location, and one to last death location. /back (with no args) will return to last death location, assuming the player has eternalcore.back and eternalcore.back.ondeath permission. If only one is present, the player should be teleported to the one it does have permission to.

The /back command will also have death and teleport arguments to let the player pick which location to teleport to.