Clean up and document AuditEvent API

The AuditEvent bean has an awkward API for the request URL. It exposes public StringBuffer getRequestUrl() which returns a StringBuffer of the url up to the query part. This patch will replace that with a public String getBaseUrl(). We will also add a public String getUrl() method to get the full request URL including query parameters.

Also need to add JavaDocs to all getters in AuditEvent