Replace URL with local refs and small fixes

* Remove stop_time from job meta
* make Unit use unit.schema in cluster.json

datastructures/unit.schema.json

@@ -1,11 +1,11 @@
 {
     "$schema": "http://json-schema.org/draft/2020-12/schema",
-    "$id": "https://raw.githubusercontent.com/ClusterCockpit/cc-specifications/master/datastructures/unit.schema.json",
+    "$id": "unit.schema.json",
     "title": "Metric unit",
     "description": "Format specification for job metric units",
     "type": "object",
     "properties": {
-        "base_unit": {
+        "base": {
             "description": "Metric base unit",
             "type": "string",
             "enum": [
@@ -36,6 +36,6 @@
         }
     },
     "required": [
-        "base_unit"
+        "base"
     ]
 }