WIP: refactor for new reflex-based qua-view, includes qua-types

[mb21]

TODO:

• [ ] test various authentication and redirect flows
• [ ] make sure we use currentScenario instead of scenario at all the right places
• [ ] make sure old links, shared on e.g. fb, are redirected
• [x] consistently rename scenarioProblem to exercise
• [ ] put in the following message at the right place: https://github.com/achirkin/qua-kit/blob/e4cc59da366e604f7420a1110ccfb7c21145d15b/apps/hs/qua-server/src/Handler/Mooc/SubmitProposal.hs#L70
• [x] add og:links back in
• [x] rename and import QuaTypes qualified
• [ ] ...?

For ce1854b, the following migration is needed:

ALTER TABLE "scenario_problem"  RENAME TO "exercise";
ALTER TABLE "scenario"          RENAME COLUMN "task_id" TO "exercise_id";
ALTER TABLE "current_scenario"  RENAME COLUMN "task_id" TO "exercise_id";
ALTER TABLE "problem_criterion" RENAME TO "exercise_criterion";
ALTER TABLE "problem_criterion" RENAME COLUMN "problem_id" TO "exercise_id";
ALTER TABLE "vote_rating"       RENAME COLUMN "problem_id" TO "exercise_id";
ALTER TABLE "rating"            RENAME COLUMN "problem_id" TO "exercise_id";