Added optional client auth by shared secret (also modified schema, client, curl client). Modified Client __str__ method for log display without disclosing secret. Modified wsgi server logging and parameter disposing accordingly.

Clients are now authorized by client= argument in URL, schema and client lib is updated accordingly. Method authentication defined in "expose" decorator. Added Client container class for deterministic logging. Schema update to consistent InnoDB and utf8mb4 everywhere.

Error is now raised via req.error helper, which automatically adds already known info (method, request id), thus calls are terser.
Client's Error communicates request id, if received from server.
exc_info made explicit everywhere. Automatic exc_info gathering sometimes returned bogus info about unrelated exception from far before.

Fixed multiple HTTP args encoding/parsing, store_event now uses SQL placeholders, more robust fetching of cat/tag in store_event, simplified map_id usage