IMP-1156: Add CatalogServer API for listing all UDFs and UDAs in a database

Adds a new client API for retrieving all user defined functions (aggregate and scalar)
in a database. This is a requirement from CM Backup Disaster and Recovery.

Change-Id: I4e33d714795fe808370262f36218ea112f67ec30
Reviewed-on: http://gerrit.ent.cloudera.com:8080/1271
Reviewed-by: Nong Li <nong@cloudera.com>
Tested-by: jenkins