Improve LOGGER levels in Memoizer

Various conditions in Memoizer were being logged
at DEBUG when they were really error or at least
exceptional states. This corrects most of them.
There is still some question of what should be
at TRACE and what at DEBUG.

Also, one log statement was being reached if the
condition didn't hold. This is now checked by an
if/else.

See:
https://www.openmicroscopy.org/community/viewtopic.php?f=4&t=7548
merge dev_5_0 -D org: PR 1231 (Update version history for 5.0.3)
merge dev_5_0 -D org: PR 1238 (Autogen: prevent ClassNotFoundException from being needlessly thrown)
merge dev_5_0 -D org: PR 1240 (Fix ImageAcquisitionDate parsing for DeltavisionReader)
merge dev_5_0 -D org: PR 1246 (Improve LOGGER levels in Memoizer)
merge dev_5_0 -D org

Repository: openmicroscopy/bioformats
Excluded PRs:
  # PR 1230 melissalinkert 'Update version numbers to 5.0.3' (label: exclude)
Already up-to-date.

Merged PRs:
  # PR 1231 melissalinkert 'Update version history for 5.0.3'
  # PR 1238 melissalinkert 'Autogen: prevent ClassNotFoundException from being needlessly thrown'
  # PR 1240 sbesson 'Fix ImageAcquisitionDate parsing for DeltavisionReader'
  # PR 1246 joshmoore 'Improve LOGGER levels in Memoizer'

Generated by OME-5.0-merge-push#155 (http://ci.openmicroscopy.org/job/OME-5.0-merge-push/155/)