TMSS-1218: Add parsets to SIPs and refer to the primary observation subtask as ObservationID (former 'SAS VIC Tree Id')

TMSS-1216: we foresee more problems when draft can be NULL, then when we enforce the link to stay which guarentees that we can follow the path_to_project for blueprints

TMSS-1124: fix for new schema, define scheduling_unit_observing_strategy_template as object with name/version

TMSS-1124: not all strategy templates were tested because some were skipped due to lacking scheduling_contraints. Enforce that the scheduling_constraints_template is defined by name and version. This makes some templates/tests fail, which are fixed in next commits by complying with the new schema

TMSS-605: Add check for stations in use when saving reservation, and fix reservations tests which were a no-op so far

TMSS-1121: added convenience is_obsolete property to TaskBlueprint. Ignore obsolete tasks in specifications_doc_including_copies_for_failed_tasks

TMSS-778: Add error_reason field to Subtask model; update filterset and serializer for the Subtask model

TMSS-780: task obsolete_since is None is non-obsolete subtask exists, task status ignores obsolete primary subtask, SU status ignores all obsolete tasks

TMSS-1003: Add 'unschedulable' status to SUB and TaskBlueprint and propagate its value from Subtask upwards