Internationalization fixes to automatic playlist UI

I'm not sure if the contexts for translators are good enough, but at least the strings are now technically translatable, apart from the entries in genre, mood and style lists. They aren't currently translatable.

Testing done: Made a new automatic playlist with different types of filters, then quit Tomahawk and started it again. Then checked that the filter UI displayed correctly, meaning that the type selector combo box state and other elements, also the sentence summary, were correct. Updated the Finnish translation locally and checked that the translations appeared correctly.