PP-663 (Partial): Reduce logging volume

[io7m]

What's this do?
This makes a couple of changes to assist with (but not solve PP-663):

• We no longer log account list icons, because some of them are still giant base64 encoded PNGs that end up in logs.
• We accept the fact that book database entries can disappear when syncing bookmarks

Why are we doing this? (w/ JIRA link if applicable)
Affects: https://ebce-lyrasis.atlassian.net/browse/PP-663

How should this be tested? / Do these changes have associated tests?
Nothing, really. There's just less noise in the logs now.

Dependencies for merging? Releasing to production?
None.

Have you updated the changelog?
N/A

Has the application documentation been updated for these changes?
N/A

Did someone actually run this code to verify it works?
@io7m Enjoyed the peace and quiet.