Adding in text strings for import export.

calendar/resources/locale/en-US/calendar.properties

@@ -50,6 +50,13 @@ addDuplicate=Add duplicate entry:
 #spaces needed at the end of the following lines
 eventTitle=Title:      
 eventStartTime=Start Time: 
-eventEndTime=End Time:   
+eventEndTime=End Time: 
+eventSummary=Summary:
+eventDescription=Description:
+eventWhen=When:
+eventWhere=Where:  
 
-unableToRead=Unable to read from file: 
+unableToRead=Unable to read from file: 
+unableToWrite=Unable to write to file: 
+defaultFileName=MozillaCalEvents
+HTMLTitle=Mozilla Calendar