TMSS-173: simplified validation of json_strings against schema's. The original design (proof-of-concept) had the validation in the Subtask class, and the suggestion/goal of this ticket TMSS-173 was to change that into a reusable mixin. Using a mixin is certainly possible, and the 1st implementation in this ticket was a good start, but it also showed that the whole class/mixin based approach requires too much administration (keeping track of which fields to use). This new solution with just a validation method is far simpler, and just as reusable.

Resolve TMSS-162

Closes TMSS-162

See merge request !109

TMSS-162: Fix bug in unittest setup that silently lets broken tests pass (error in range definition)

TMSS-162: Add user reference to subtask and log on save to also log creation and updates through ORM

Cannot run OIDCSession-test when OIDC_RP_CLIENT_ID is not set in the environment to configure django settings

Resolve TMSS-146

Closes TMSS-146 and TMSS-163

See merge request !104

Resolve TMSS-163

See merge request !110

TMSS-163: removed obsolete SubSystems/RAServices/Dockerfile. Please use Docker/lofar-ci/Dockerfile_lofar_sas from now on (which is also used in .gitlab-ci.yml