orm type should be specified at Repository level (#856)

[etj]

Overview

Add the server instance in context so that custom Repository can manage its properties

Related Issue / Discussion

• Issue orm type should be specified at Repository level #856
• PR for master: orm type should be specified at Repository level (#856) #864

Additional Information

Contributions and Licensing

(as per https://github.com/geopython/pycsw/blob/master/CONTRIBUTING.rst#contributions-and-licensing)

• I'd like to contribute the feature discussed in Fix recobj referenced before assignment #865 to pycsw. I confirm that my contributions to pycsw will be compatible with the pycsw license guidelines at the time of contribution.
• I have already previously agreed to the pycsw Contributions and Licensing Guidelines

[tomkralidis]

Thanks for the PR @etj. Are we able to PR to master branch, and then (I can) backport to 2.6?

[etj]

@tomkralidis the PR for master is at #864