Review greetings contract and add ricardian clauses

[gaboesquivel]

• [ ] improve the contract so that you don't have to send your username as param, we want to get that from the EOS account that's signing the contract.
• [ ] add ricardian clauses

[gaboesquivel]

ref ricardian automation script https://github.com/eoscostarica/eos-local/pull/58/commits/f7931affabf199536ea272ea5dc6861ced00f920

ref old contract https://github.com/eoscostarica/eos-local/tree/3c4757516c7cad2e697fb8f1b1eba5e8fb9cd779/contracts/eoslocal

[gaboesquivel]

not necessary for this demo