[#469] Add ticket helpers

Description

Problem: it is not immediately obvious what tickets are for and how to use them properly. Moreover, existing instructions for working with tickets are quite low-level, there are apparent common primitives that would be useful for most of the contract that decided to rely on the tickets feature.

Solution: add a dedicated module with high-level primitives and developer notes that describe the motivation beyond those.

Related issue(s)

Related to #469 (closed)

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