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.