Replace prints with (debug) logger

[bbonf]

There are several places in the library where print() is used for warnings, errors or debug messages. That's convenient for local development but not when deployed on a server as part of GrETEL.

Specifically https://github.com/UUDigitalHumanitieslab/mwe-query/blob/develop/mwe_query/lcat.py#L189 seems to be happening often and overflowing logs that no one reads.