Adding in text strings for import export.

calendar/locales/en-US/chrome/calendar/calendar.properties

@@ -51,5 +51,12 @@ addDuplicate=Add duplicate entry:
 eventTitle=Title:      
 eventStartTime=Start Time: 
 eventEndTime=End Time: 
+eventSummary=Summary:
+eventDescription=Description:
+eventWhen=When:
+eventWhere=Where:  
 
 unableToRead=Unable to read from file: 
+unableToWrite=Unable to write to file: 
+defaultFileName=MozillaCalEvents
+HTMLTitle=Mozilla Calendar