downcase all 'localized' key names to match the rest of index-v1

downcase all 'localized' key names to match the rest of index-v1

This is a little omission.  keys that are used in metadata/*.yml all start
with an UpperCase letter, but in fdroidserver, index-v1.json, and
fdroidclient, it is all camelCase with lowercase first letter. The keys
from the 'localized' section are currently never in metadata/*.yml, so
these keys never get downcase.  This change will break fdroidclient
versions that do not also have this change, but since we're in alpha, that
should be fine.

If support for a 'localized' section is added to metadata/*.yml, then the
keys there should probably be UpperCase CamelCase to match the other keys.