Integrate i18n/Stringsdict support for Activities titles and subtitles

[marcpalmer]

[marcpalmer]

Actually we just need to document this. Current Apple practice means that NSLocalizedString(x, y) must be used at all call sites for genstrings to work unless they use custom matching templates. Therefore we can't do anything too smart for people who want to use genstrings

[marcpalmer]

There is already a solution - implement prepareActivity and/or .ActivityMetadataRepresentable and use whatever i18n string mech you would normally use. We can punt a smarter solution for this to a later release (if we ever really need it). Ideally it would be nice to automatically create these using template strings that are localised using conventions e.g. a string with ID activity.title.YourTypeName