Add built in macro {ITEM.TIME[0-9]} and {ITEM.LASTTIME[0-9]} that contains the timestamp of the trigger item

The {ITEM.*} built in macros are extremely useful in trigger definitions in particular the trigger description.

We use them in the trigger descriptions like:

          *** Trigger Values ***

          _          _Block Device Statistics - Utilisation %: {ITEM.VALUE1}

          _          _*** Latest Values ***

          _          _Block Device Statistics - Utilisation %: {ITEM.LASTVALUE1}

The above works for sample/count based triggers where you say fire if the last #3 samples are xxx.

However for nodata() where you test whether data has or has not been received it would be nice to be able to display the last item collection time for example:

          *** Trigger Values ***

          _          _Zabbix Agent Ping - Response Time: {ITEM.TIME1}

          _          _*** Latest Values ***

          _          {}Zabbix Agent Ping - Response Time{}: {ITEM.LASTTIME1}{_}

The would mean the end user would be able to know exactly when it last collected data.