Add an index for lookup by account to log entries

Also fixes the query to require one less join

data/database.py

@@ -730,10 +730,9 @@ class LogEntry(BaseModel):
     database = db
     read_slaves = (read_slave,)
     indexes = (
-      # create an index on repository and date
+      (('account', 'datetime'), False),
+      (('performer', 'datetime'), False),
       (('repository', 'datetime'), False),
-
-      # create an index on repository, date and kind
       (('repository', 'datetime', 'kind'), False),
     )