Adjust logging of setId

ImageReader now logs setId at INFO, while FormatReader logs setId at
DEBUG.  This means that the top-level call to setId should show up by
default, but setId on any constituent files (e.g. TIFFs in a plate) will
only show up if the log level is changed to DEBUG or TRACE.

This should substantially clean up the INFO-level logs for multi-file datasets.
Merge pull request #541 from melissalinkert/setid-logging

Adjust logging of setId