Metadata jackets: Use a safe formatter

Metadata jackets: Do not error out when using a custom template with
some custom fields that are not present. Fixes #1225357 [polish fails when adding jacket to epub](https://bugs.launchpad.net/calibre/+bug/1225357)
Merge branch 'master' of https://github.com/cbhaley/calibre
Book details: Render custom comments fields correctly

Book details panel: Render custom comments fields the same as the builtin
comments field. In particular this fixes problems caused by wide text and
images in custom comments fields. Fixes #1226350 [Image in Custom Comments Column](https://bugs.launchpad.net/calibre/+bug/1226350)
Sage News - Satire by Brian Hahn

Fixes #1226417 [[Enhancement] New Publication Recipe - The Sage News - Satire](https://bugs.launchpad.net/calibre/+bug/1226417)
Sage News - Opinion by Brian Hahn

Fixes #1226420 [[ENHANCEMENT] New Publication Recipe - The Sage News - Opinion](https://bugs.launchpad.net/calibre/+bug/1226420)
Allow an icon rule to put multiple icons on a column