TMSS-745: extract scheduling_constraints_doc and scheduling_constraints_template from submitted template and use it.

TMSS-745: when no such template available... get a list of all templates and print it, so the user can lookup the one that he wants

Resolves TMSS-841

Closes TMSS-841

See merge request !510

TMSS-876: include Access-Control-Allow-Methods in response headers to hint to...

Closes TMSS-876

See merge request !506

TMSS-745: handle trigger submission in one transaction. If anything fails, the whole trigger is discarded.

TMSS-745: removed initial test for triggers. This endpoint does not exist anymore. Added SubmitTriggerTestCase. Added test_create_draft_from_all_strategy_templates.

TMSS-745: use the new functionality from the refactored strategy templates to construct a valid trigger doc, and submit it to tmss

TMSS-745: added two methods to 1. get a trigger specification document, and 2. use the (edited) trigger doc for submitting

TMSS-745: added various convenience endpoints on the SchedulingUnitObservingStrategyTemplate to get various versions of the template document: plain, complete_with_all_defaults, just_with_the_parameters. Can be used to construct json documents to upload as schedulingunitdraft or for triggers