Update schema command names & Implement displaying schemas more user friendly

[jakub014]

Update schema related command names to smth like:
--avro-schema for the avro schema (currently --topic)
--schema for more readable schema <-- to be implemented
--update-schema:= updates schema (formerly --schema)

[jakub014]

The simplified schema is implemented here

[jakub014]

The feature will be merged once the overhaul of parsing commands is ready.