major improvements and rework

- add stream / instrument availability data
- events contain event kind for dispatching db methods

nicoscache.py

@@ -156,7 +156,6 @@ class NicosStream(Stream):
         except Exception as e:
             print(self.uri, repr(e))
             return
-        cnt = 0
         for ts, devname, param, op, value in sorted([t, d, p, o, v] for (d, p), (o, v, t) in events.items()):
             descr = self.descr.get(devname)
             mod = descr.get('secop_module', devname) if descr else devname
@@ -164,11 +163,9 @@ class NicosStream(Stream):
             if self.devices.get(devname):
                 try:
                     value = self.convert[key](value)
+                    yield 'value', value, key, self.tags, ts
                     error = None
                 except KeyError:  # no conversion function
                     continue
                 except TypeError:
-                    value = None
-                    error = 'error'
-                cnt += 1
-                yield key, value, error, ts, self.get_tags(key)
+                    yield 'error', 'error', key, self.tags, ts