Linear tickets

This MR contains a simplified implementation of tickets that rely on linear typing (tickets are forbidden in DUP) instead of the global storage of MR !326 (closed).

The visible differences for Michelson devs are:

• the OWN and PUNCH instructions have been removed,
• the ticket_handle type has been renamed to ticket,
• READ_TICKET always succeed (returns the triple directly instead of an option),
• at type-checking, DUP checks that it is not duplicating a ticket (some gas is consumed for this).

Pros:

• tickets are probably easier to manipulate in this setting because the devs cannot shoot themselves in the foot by forgetting a OWN or pay unnecessary storage by forgetting to PUNCH,
• the code is much simpler.

Cons:

• the constraint on DUP might be hard to fulfill for compiler developers,
• relying on the Michelson type system to preserve invariants might complicate future migrations to unlinear type systems.