Full support for land claim blocks in import/export

[djkrose]

When exporting and importing land claim blocks, they should be properly saved and restored with an additional entry in the global LCB registry of PersistentPlayerData, so that the imported LBC's are fully active.

When LBCs are removed by overwriting them with something else using dj-import, they should be unregistered from their corresponding PersistentPlayerData.