Remove healthcare datatypes from datawarehouse tables.

Using only basic datatypes enables a broader set of target datawarehouse
options.
Separate the database into a pre-staging, staging and dwh database.
WIP update etl from staging to a remote dwh.

The ETL process that runs on the staging database will generate a local
changeset for dimension and fact tables, that can be used by the datawarehouse
loader to insert facts and merge new dimension information.
Revert white-space errors of the previous commit, small fixes.
Small cleanups:

- Put dwh tables in staging database in separate schema dwh.
- Change dblink foreign server:
  - use CURRENT_USER instead of fixed mgrid user
  - use dblink_fdw as server type instead of pg
- Put all search_path settings in create_staging.sh script.
- Put all extension creation in create_staging.sh script.

Note: the last two steps must be repeated for the pre-staging script.
Add ancestor information to dim_concept to facilitate hierarchical queries.
Reduce computation in updating the time dimension.
Remove DEFAULT columns from dwh tables.
Add gp loaders for dimension and fact changesets.
Remove comment to enable transforming coded facts again.
Improve ETL speed.
Accept PQ units with m^2 by replacing them with m2.

This is a workaround, until either PQ supports m^2 notation, or the generated
documents do not contain these codes anymore.
Add local terminology mapping to SNOMED-CT.

This is an ad-hoc method that consists of a simple table with the mapping,
currently only some of the Portavita local codes to SNOMED-CT.  Can be replaced
with a method that queries a central terminology service.
Add some workarounds to errors in generated cda documents.
Enable to block context conduction.
Improve ETL of coded facts. Add codesystem to terminology mapping.

Instead of calling per-row dimension lookup functions, the most expensive
lookups are now replaced with joining the dimensions in the range table
instead.  For the sake of loose coupling, the API functions xxx2set_nk are
still used, but a bit rewritten to be better performing, at the loss of
generality.

This commit adds the codesystem to the terminology mapping table.  Todo is
adding the codesystem version.
Add loading staged data to PostgreSQL databases.

A new script was added that takes a gpload yaml script, and merges or inserts
data to the dimensions and fact tables in a PostgreSQL database.

Since file_fdw is used, this commit creates a dependency to PostgreSQL >= 9.1.