Update Liebert.events.xml

After a few hours of work I finally was able to compile all Liebert MIBs (http://ask.opennms.eu/?qa=305/solve-cannot-find-symbol-displaystring-error-while-compiling)
There are 9 "new" events. They were included in LIEBERT-GP-NOTIFICATIONS-MIB and LIEBERT-GP-SYSTEM-MIB (www.emersonnetworkpower.com/en-US/Brands/Liebert/Pages/TheLatestMIBsAvailableforDownloads.aspx)