create LogHandler for the dashborad

- simple memory log handler which stores the last
  64 warnings/errors for the dashboard

app/src/web/log_handler.py

@@ -0,0 +1,24 @@
+from logging import Handler
+from logging import LogRecord
+import logging
+from collections import deque
+
+from singleton import Singleton
+
+
+class LogHandler(Handler, metaclass=Singleton):
+    def __init__(self, capacity=64):
+        super().__init__(logging.WARNING)
+        self.capacity = capacity
+        self.buffer = deque(maxlen=capacity)
+
+    def emit(self, record: LogRecord):
+        self.buffer.append({
+            'ctime': record.created,
+            'level': record.levelno,
+            'lname': record.levelname,
+            'msg': record.getMessage()
+        })
+
+    def get_buffer(self, elms=0) -> list:
+        return list(self.buffer)[-elms:]