DS 2381 sitemap generator skip unreadable items

see [DS 2381](https://jira.duraspace.org/browse/DS-2381)

added a new Console appender in log4j.properties such that all log DEBUG calls from org.dspace/app appear on the console as well as  dspace.log 

personally I find the standard command line utilities rather quiet - I like tracing to assure me that what is happening is actually what I think should be happening