Changed the definitiosn to get the following benefits:
Changed the definitiosn to get the following benefits:

1. You can define an interface with the string names. This will:
     a. Provide better auto-complete (with your string names)
     b. If you do not define a string as optional, you will get a compile
        error if you forget to include it in one or more language

2. The property of the LocalizedStrings class is a string (and not string|function)
   as it was before, so it can direcly be assigned to a string (the previous
   version caused a compile error since string|function can not be assigned to string

stefalda/ReactNativeLocalization,stefalda/ReactNativeLocalization,stefalda/ReactNativeLocalization,stefalda/ReactNativeLocalization