Refactors alerts and flow statuses in builtin and plugins

Implements #3811
Implements #3812

Refactors builtin alerts

Refactors builtin flow statuses

scripts/lua/modules/alert_definitions/alert_influxdb_error.lua

@@ -0,0 +1,16 @@
+--
+-- (C) 2019-20 - ntop.org
+--
+
+local alert_keys = require "alert_keys"
+
+local function formatInfluxdbErrorMessage(ifid, alert, status)
+  return(status.error_msg)
+end
+
+return {
+  alert_key = alert_keys.ntopng.alert_influxdb_error,
+  i18n_title = "alerts_dashboard.influxdb_error",
+  i18n_description = formatInfluxdbErrorMessage,
+  icon = "fas fa-database",
+}