localization fixes

Merged username-removed-24982 requested to merge eighthave/fdroidclient:localization-fixes into master

This is three fixes for displaying the localized index metadata properly, and one new test suite for finding bad formats in translated strings that can often cause crashers, and at the very least, end up with incorrect text display.

With this merge request, fdroidclient should now handle all of the metadata that can come from !253 (merged). That means all the metadata that fastlane supply and Triple-T Gradle Play Publisher support.