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

server/server.js

@@ -219,6 +219,7 @@ let needSetup = false;
                 bean.url = monitor.url
                 bean.interval = monitor.interval
                 bean.hostname = monitor.hostname;
+                bean.maxretries = monitor.maxretries;
                 bean.port = monitor.port;
                 bean.keyword = monitor.keyword;