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_am_threshold_cross.lua

@@ -0,0 +1,64 @@
+--
+-- (C) 2019-20 - ntop.org
+--
+
+local alert_keys = require "alert_keys"
+
+local format_utils = require("format_utils")
+local json = require "dkjson"
+
+local function thresholdCrossFormatter(ifid, alert, info)
+   local alert_json = json.decode(alert.alert_json)
+
+   local msg
+   local host = alert_json.host
+   local numeric_ip = info.ip
+   local ip_label = host and host.label or numeric_ip
+
+   if numeric_ip ~= ip_label then
+      numeric_ip = string.format("(%s)", numeric_ip)
+   else
+      numeric_ip = ""
+   end
+
+   if(info.value == 0) then -- host unreachable
+      msg = i18n("alert_messages.ping_host_unreachable_v3",
+		 {host = ip_label,
+		  numeric_ip = numeric_ip})
+   else -- host too slow
+      if alert_json.operator == "lt" then
+	 i18n_s = "alert_messages.measurement_too_low_msg"
+      else
+	 i18n_s = "alert_messages.measurement_too_high_msg"
+      end
+
+      local unit = "active_monitoring_stats.msec"
+
+      if alert_json.unit then
+	 unit = alert_json.unit
+      end
+
+      unit = i18n(unit) or unit
+
+      local msg_table = {
+	 host = ip_label,
+	 numeric_ip = numeric_ip,
+	 am_value = format_utils.round(info.value, 2),
+	 threshold = info.threshold,
+	 unit = unit,
+      }
+
+      msg = i18n(i18n_s, msg_table)
+   end
+
+   return msg
+end
+
+-- #######################################################
+
+return {
+  alert_key = alert_keys.ntopng.alert_am_threshold_cross,
+  i18n_title = "graphs.active_monitoring",
+  i18n_description = thresholdCrossFormatter,
+  icon = "fas fa-exclamation",
+}