With the new localization support, the name/summary/description in the
metadata file becomes the global override. So most apps are not going to
have those fields present in their metadata file. This fixes the index.xml
generation to fall back to the localized versions of those fields when they
are not set in the metadata field.
https://forum.f-droid.org/t/what-has-happend-to-osmand
This allows a source repo to include a complete metadata file so that it
can be built directly in place using `fdroid build`. If that app is then
included in fdroiddata, it will first load the source repo type and URL
from fdroiddata, then read .fdroid.yml if it exists, then include the rest
of the metadata as specified in fdroiddata, so that fdroiddata has
precedence over the metadata in the source code.
This lets `fdroid build` apps without having a whole fdroiddata setup, but
instead just directly in place in the source code. This also lets devs
optionallu maintain the fdroid metadata as part of their app, rather than
in fdroiddata without loosing any control. This should make it easier to
spread around the maintenance load.
