Do not use PSQL arrays anymore. They caused "major" headaches when quoting
array of strings. An array of strings is now stored as a normal string
delimited by '[' and ']', just as in a ParameterSet.

- API change: renamed work_order to command to conform with control terminology.

- API change: added get_next_step() that gets the next work order that is also a step. It
  returns both the work order id and the attributes of the step (iface_step).

- API change: get_step() and get_solve_arguments() now return only parset related columns.

- API change: add_step should be considered private. Always use one of add_{predict, subtract, correct, solve}_step().
  This will ensure database consistency.

- changed API: add_solve_arguments -> add_solve_step, so API ensures consistency (i.e.
  with the change it is harder to add a solve step without solve arguments.

- API change: names of the columns returned by e.g. get_step() now match the names in the parset precisely.

Moved sql scripts from src to sql directory.

- Initial check in of the database side of the black board. Includes table definitions,
  triggers, and an API in the form of a collection of stored procedures.