[issue 2] First implementation of a ticket minting contract

[pecornilleau]

PR DRAFT

• implements mint_sc
• implements https://github.com/marigold-dev/chusai/issues/2
• to build make build
• to test make test

A directory mint is added in part L1 of the repo. It contains a contract implementing issue 2. The parameter types of the smart contract are added into L1\commons\mint_part.mligo, synchronisation with wallet_sc to come. A few test utilities are provided, as a proposal to bring testing tool to the project. In `L1\mint\test\test_utils.mligo"

[rueshyna]

I read words like smthg, nb. could we not use abbreviation? (It will save my day :pray:.)