Install the mumble VoIP client

Tails Server will make it easy to run a mumble server, so we probably should ship mumble in Tails.

There has been some discussion about this on #11241 (closed) that should be summarized here. Since then a patch has been upstreamed which exposes the SSL certificate’s fingerprint on the initial prompt when a cert failed to validate (e.g. because it was self-signed, which will be the case when Tails Server hosts a mumble server). We should try to get that patch backported to Debian Jessie.

team: segfault, sajolida

Parent Task: #5688

Related issues

• Related to #5709
• Related to #14568 (closed)
• Related to #15543

Original created by @anonym on 11551 (Redmine)