Remove UI string resources from library

These string resources were used to set the title and buttons of NumberPickerDialog but that doesn't work well for localization as the library can't provide these string resources in all languages that a user of the library might want to localize an app to, and furthermore would the proper localizaton also sometimes depend on context.
    
Instead, require these strings to be passed as arguments to the NumberPickerDialog constructor. Even for non-localized apps this provides greater flexibility for the user of the library.