Added statistics recording to API
(required changes in DSpace API!)

Also some changes to make REST API work better with XML output.
Added Checksum and sequenceId to Bitstream.
added licence header
corrected 'items' and 'parentCommunityList' in return.
Added usage events for collections view and communities view
Merge pull request #356 from AnjaLeBlanc/DS-1719

DS-1719 Added statistics recording to Jersey-REST API