Ignore --schema (with warning message) if --state-file provided

[yshalenyk]

state-file contains all columns and data based on previous schema analysis. But there its unclear how to behave when user attempts to override schema with --schema but also provides old --state-file.
Two options I see:

• ignore --schema when --state-file is provided (now)
• reanalyze file with new schema

[jpmckinney]

I think it's fine to ignore --schema (with a warning message).

I assume a common workflow might be to specify --schema on a first run, and then the user might add --state-file on a second run, and forget to remove --schema.

I think it is less likely that a user creates a state file, and then decides to change the schema.