Add a phone filter on the campaign

Becasue we can have multiple phones associated to a Contact, we might want to provide a way to filter them to only expose the one needed.

For instance, MEPs have two phones (one for Brussels, one for Starsbourg), but we want to call them in Brussels.

The filter would be a string which should match the phone number exposed by the Contact View. For instance, to discriminate between Strasbourg (France) and Brussels (Belgium), the former would match +33.* (France internayional number) and the later would match +34.* (Belgiulm).

If the filter is an empty string, the campaign shoudl return the first number it has.