Handle translation files correctly

[simonseyer]

Right now translation folders (.lproj) are just added as groups to the project and the .strings files are just copied over to the bundle. This leads to the .strings files overriding each other because they have the same name (e.g. Localisable.strings) and are put into the same folder (the root of the bundle).

In addition they are not correctly rendered by Xcode.

Potential solution: CocoaPods/Xcodeproj#85 (comment)