Let a proposed record be withdrawn (issue 1081)

A dropped proposal or a stale reservation stayed proposed forever: there was
no way to say the operator decided against it. knowledge-base.withdraw takes
a reserved or proposed record to withdrawn as a new version naming why, ends
a waiting operator's ask and clears a pending review in the same version,
and refuses an already accepted, superseded or withdrawn record. The number
stays spent either way.

The old Withdraw (the background job for reservations never proposed) is
renamed WithdrawStale to make room for the new, caller-driven WithdrawRecord.

modules/mesh-knowledge/module.json

@@ -31,7 +31,8 @@
         "reserve",
         "propose",
         "import",
-        "return"
+        "return",
+        "withdraw"
       ]
     }
   ],
@@ -50,7 +51,8 @@
         "reserve",
         "propose",
         "import",
-        "return"
+        "return",
+        "withdraw"
       ]
     }
   ],