Simulate a remove event at the site on deletion of a top level community

Fixes DS-1966
Merge pull request #517 from pnbecker/DS-1966

Simulate a remove event at the site on deletion of a top level community
Update clean-database to drop additional tables

Updates clean-database.sql file to drop tables recently added to the
DSpace project:

-  webapp, webapp_seq
- requestitem, requestitem_seq;
Merge pull request #540 from keithgee/clean_database_update

Update clean-database to drop additional tables