Add a 'Slow connection' warning. Use perf_counter() in place of time()

and also lower the _CHUNK in the database download thread

constants.py

@@ -52,6 +52,8 @@ class Messages:
     NO_CONNECTION_MSG        = "Unable to establish an internet connection."
     BAD_DOWNLOAD             = "Something went wrong"
     BAD_DOWNLOAD_MSG         = "Something went wrong with the downaload.\nCheck your internet connection and try again."
+    SLOW_CONN                = "Slow internet connection"
+    SLOW_CONN_MSG            = "Your internet connection is unstable or too slow."
 
 
 class Signal: