Trunk 4446: Support deriving auto_expire_date from duration and duration units for Drug Orders

Changes for ticket https://issues.openmrs.org/browse/TRUNK-4446
Since we are going to use a known uuid for referring to this concept source, the chances of some one else already creating this source would be zero. Precondition would be unnecessary here.

Also in the docs they talk about preconditions while add/drop of tables, columns, constraints.  There is no mention of the data. In fact most of the <insert> change sets in same file do not have pre condition.