Update the Mecenas example to cover contract bug

[mr-zwets]

The Mecenas contract allows for multiple contract inputs but this can lead to behavior as pointed out in telegram, we should update the examples & docs, and also the the Mecenas contract used in the automated tests

[mr-zwets]

further the mecenas contract has the actual relative timelock logic commented out

@kiok46 noticed it would best to restore this now that we have working tests for MockNet with local evaluation.
However, this raises a further question: how in the scenario can the UTXO age be set as to make succeeding and failing tests for relative locktime checks