add retries for pinging function

backend:
- new field for monitor: maxretries
- new pending status while service is retrying: 2
- pending status event is not marked important
- pending pings however register as downtime in the calculation

frontend:
- added pending status while service is retrying
- added color for new pending status
- added field to configure amount of retries

database:
- IMPORTANT: THIS REQUIRES MIGRATION!!!!
- added field: maxretries with default value 0

src/mixins/socket.js

@@ -274,6 +274,11 @@ export default {
                         text: "Down",
                         color: "danger"
                     };
+                } else if (lastHeartBeat.status === 2) {
+                    result[monitorID] = {
+                        text: "Pending",
+                        color: "warning"
+                    };
                 } else {
                     result[monitorID] = unknown;
                 }