Add LuaRecord.label

[TBC_x]

I'm working on a mod where I do light blueprint manipulation and I've realized that LuaRecord does not have a way to extract the blueprint label, like its LuaItemCommon counterpart

[FoxLBA]

I faced exactly the same problem in my mod.
I use export/import as a workaround, but this can cause significant lag when processing large blueprints.

[Rseding91]

Label and planner_description read/write are added for 2.1.