Doc: Add DBSS message to query for presence of an object.
Tests: Add unittest for new database message.
DBSS: Implement message to query whether an object is active.
Tests: Fix a few typos in test_dbss.
Tests: Add DBSS test for verifying that GET_ACTIVATED is FALSE after DELETE_RAM.
Merge pull request #180 from Astron/feature/dbss-get-metadata

Feature: DBSS message to query for object activation.