Record lamp technology type (led / halogen / cfl / ...)

Station prompts for it (default led), metrics.json carries it as
'type', and the scaffolded device page description and Type spec
follow it.

lamp_export.py

@@ -178,6 +178,9 @@ def write_bundle(reading, out_dir, meta, n_readings, supply=None):
     metrics = {"name": meta["name"]}
     if meta.get("ean"):
         metrics["ean"] = meta["ean"]
+    if meta.get("type"):
+        # Lamp technology: led, halogen, cfl, incandescent, ...
+        metrics["type"] = meta["type"]
     if meta.get("variant"):
         metrics["variant"] = meta["variant"]
     if meta.get("rated"):