define service_longname when service specified

[Audionut]

fixes #56

If --service is argumented, service_longname is not set in the meta causing error

Upload-Assistant/src/trackers/MTV.py

Line 372 in 69c0bce

if str(meta['service_longname']) != "":

I'm really lost as to what the intended purpose was here. If I just keyed like the existing logic, it would key from the first key, and just use CR, being the first key, instead of the services long name, Crunchy Roll, (since every service long_name key is duplicated from an abbreviated service key).

If I manually set --service "Crunchy Roll", then it would use "Crunchy Roll" for both the service and service_longname meta.

What on earth was the purpose of service_longname if it's just set as the abbreviated service name.......And if you service the longname, why didn't it use the abbreviated service name for the service meta.

This PR sets the service longname to the actual service longname when the argument --service is used.