add --server parameter
also change server in submission url if requested

mm.musicbrainz.org is part of the submission url given by libdiscid,
but this is now just a forwarding to musicbrainz.org for that purpose.
we should accept new and old submission urls

This is only relevant, since we change part of the url.
allow pre-selected release

This allows skipping the release choice dialog and selecting
a release with a MusicBrainz ID given as parameter.

The disc ID still has to be attached to the selected release.
Merge branch 'server'

see pull-request #64
Merge branch 'release_id'

see pull-request #65