Make printer print pretty contracts

Clarification and motivation

As result of TM-58 we have a printer of Michelson contracts which prints everything on one line because it's easier to do so. But it's not quite readable, so it would be good to pretty print contracts, so that each instruction occupies its own line, they are indented, etc.

Acceptance criteria

morley print should pretty print contracts, so that each instruction occupies its own line, they are indented, etc.