Increment version number when updating statistics in P_STATISTIC.UPDATE_STATISTIC.
Corrections to ASR_RETURNEES maintenance procedures.

Remove redundant parameter pnSTG_VERSION_NBR in procedure UPDATE_ASR_RETURNEES.
Correct UNHCR-assisted statistic type code from REFRTN_AH to REFRTN-AH. Allow
zero-valued statistics to be stored.
Add new view STC_GROUP_ATTRIBUTES. Correct name of foreign key.

Foreign key FK_STIG_STCG renamed to FK_STIG_STG.
Changes to ASR views.

Modify ASR_RETURNEES view to remove unused country codes and origin name and
include last updated date/time and user. Create new views ASR_STATELESS and
ASR_OTHERS_OF_CONCERN on the same pattern as ASR_RETURNEES.
Changes to P_ASR package and dependent changes in other packages

Package P_ASR:
- Allow asylum (returned from) country to be null;
- Update the primary statistics group record whenever any change is made in
  order to record the last update date/time and user. This requires the
  update version number of the primary statistics group to be passed as a
  parameter;
- Update the statistics group record covering all statistics for a given ASR
  table, year and country whenever any change is made in order to record the
  last update date/time and user. This statistics group record is automatically
  created if it does not already exist.
- Factor out private procedures SET_STATISTIC, SET_STG_ATTRIBUTE and
  GET_TABLE_STATISTIC_GROUP (two variants).

Package P_STATISTIC:
- Rename parameter pnID to pnSTC_ID throughout;
- Change logic of SET_STATISTIC procedure so that passing a null statistic
  value deletes an existing statistic rather than raising an exception;
- Set version number to D1.0.

Package P_STATISTIC_GROUP:
- Rename parameter pnID to pnSTG_ID throughout;
- Change logic of SET_STG_ATTRIBUTE procedure so that passing a null statistic
  group attribute value deletes an existing statistic group attribute rather
  than raising an exception;
- Set version number to D1.0.

Package P_BASE:
- Add mandatory subtype definitions for statistics and statistic groups update
  version numbers.
Create statistics group records for each combination of ASR table, year and country.

After loading all ASR statistics, create statistics group records for each
combination of ASR table, year and country and link them to the statistics that
they cover.
Correct package version numbers.