Enhancement for the db abstraction interface: now the system is also able to specify
and reflect in the db table column properties and constraints as unique, foreign keys (as before),
not null, default value (as before) and index creation (directly as class attribute flag).
Such column properties will be added to the data model also after first table creation
without the need for an upgrade script. This should cover the most typical
"incremental upgrade" use cases. Change in column type and dropping of tables, indexes
or constraints still has to be performed manually.
Also, flag for require view allows one to rebuild it automatically.
