admin: Improvements to micropub endpoint's photo handling. - Add `.jpg` extension to photos that don't have any extension. - Add photos in the config section instead of the body, so that the layout can put them in separate `u-photo` tags.

*.pyc
*.egg-info
.cache
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venv
tags
bower_components
node_modules
build/lib
util/messages/_cache
util/messages/_counter
dist
docs/_cache
docs/_counter
foodtruck/static
piecrust.egg-info
piecrust/__version__.py
.ropeproject