* Implement extra_properties in oracle Provider
These can be used to configure additional database-computed fields
in the config file which are returned on `get` and `query` calls
* Allow mandating properties which are not part of the output
Previously, properties which were not requested for the output
were not part of `fields`, which means that they were not passed
in to the provider as filter properties for e.g. `query()`.
This commit adds them there and introduces a new variable
`filtered_fields`, which is used for limiting the output of queries.
There is also some minor refactoring, but the existing and also the
newly written tests should avoid regressions.
* Restore previous behavior for default arguments
Bernhard Mallinger
8d377072b9