Allow an SP ServiceName per language

[Lapeth]

Currently there can be only one ServiceName tag constructed in metadata, but more are sometimes needed for different languages.

metadata.py, function do_attribute_consuming_service defines the service name as service_name = [md.ServiceName(text=text, lang=lang)]. It can probably be a list with multiple entries, one for each language, resulting in something like:

<ns0:ServiceName xml:lang="en">Some service name</ns0:ServiceName>
<ns0:ServiceName xml:lang="da">Et eller andet servicenavn</ns0:ServiceName>
...

It would be easy to check if conf.name is a list of tuples, and construct the service_name list by it, similar to how it's done in do_key_descriptor

Originally posted by @Lapeth in #377