..F....... [ZBX-8524] fixed trigger filter not being reset on the Monigoring->Events page

Before the fix:
- If you open the Monitoring->Events page, select some trigger, press "Filter" and then "Reset", the trigger will disappear from the filter but the event list will still remain filtered. Only when you press "Reset" once more will the filter be completely reset.

After the fix:
- The filter is reset properly. Additionally, to simplify the logic of the filter, selecting all hosts will no longer clear the trigger filter. This goes the same for the case when you switch a host group and all hosts are selected automatically.

git-svn-id: svn://svn.zabbix.com/trunk@48564 f4e7fd02-d210-4e34-a1e0-d4093fb66cc2